Abstract Ecological stoichiometry emphasizes that mismatches between the elemental composition of organisms and their resources can shape ecological interactions, evolutionary trajectories, and nutrient cycling. For hemiparasitic plants such as mistletoes, which draw water and nutrients from hosts while maintaining their own photosynthesis, such mismatches raise a fundamental question: To what extent do parasites mirror or diverge from the elemental constitution of their hosts, and what ecological and evolutionary consequences emerge from these differences? To address this, we measured concentrations of 14 elements in leaves of 168 mistletoe–host pairs spanning 90 species combinations across Australian bioregions. We used bioconcentration ratios, slopes of log–log relationships, and spatial mixed‐effects models to assess whether mistletoes accumulate or underaccumulate elements relative to their hosts, and to test the influence of host phylogeny, mistletoe identity, and geography on stoichiometric patterns. Mistletoes consistently exhibited higher concentrations of boron, copper, phosphorus, potassium, and sodium, but lower iron and nitrogen than their hosts, while concentrations of other elements were broadly similar. Potassium, in particular, showed evidence of tight homeostatic regulation across diverse hosts, suggesting a physiological requirement potentially linked to water relations and osmoregulation. In contrast, sodium and several other elements tracked host concentrations more closely, indicating context‐dependent accumulation. Variation in mismatches was strongly structured by host family, species pair, and site, underscoring the importance of both evolutionary and geographic context in parasite–host nutrient relationships. These patterns imply that mistletoes are not simply “what they eat” but instead selectively accumulate elements in ways that may underlie their distinctive life history traits, such as extended reproductive phenology and high transpiration rates. At broader scales, stoichiometric mismatches between mistletoes and hosts may influence herbivore foraging, shape plant–animal interactions, and alter nutrient inputs through litterfall, thereby contributing to ecosystem productivity and biodiversity. By linking elemental imbalances across individual, community, and ecosystem levels, our results highlight the integrative role of stoichiometric theory in understanding the biology of parasitic plants and their ecological consequences.

The search for predictors of plant diversity has challenged scientists for decades. Here we identify intense photosynthetically active radiation (PAR) as a major factor constraining plant species richness in global grasslands. We show that the strength of the negative relationship between species richness and PAR increases with increasing elevation and that species richness is more strongly correlated with intense PAR than with UV-B radiation, climate variables, and atmospheric nitrogen deposition. In addition to species richness, plant biomass was also negatively correlated with PAR at higher elevations, indicating that intense PAR also constrains plant biomass in montane grasslands. Furthermore, we show that the decrease in plant species richness with increasing PAR is mainly caused by a decrease in species richness of forbs, sedges, and rushes. In contrast, species richness of grasses was only negatively correlated with PAR at high elevations, and species richness of legumes was not significantly correlated with PAR. Our results suggest that PAR constrains plant species richness in global grasslands and limits the extent to which plant species of specific functional groups can migrate uphill in response to climate warming.

Questions Structurally dominant species can be especially influential in plant community assembly and ecosystem function as Species of Unusual Effect (SUEs). For example, indigenous bunchgrasses function as foundation species and ecosystem engineers in the naturally high-diversity groundcover of longleaf pine savannas. Other species structurally dominate relatively small, discrete patches across the savanna landscape, for example, the fern Pteridium aquilinum and the shrub Ilex glabra. Do patch-level species richness or composition of assemblages of groundcover plants, or of arthropods, differ between bunchgrass-dominated groundcover and groundcover dominated by P. aquilinum or I. glabra?Location We conducted our study in a restored longleaf pine savanna in southeastern Louisiana.Methods We compared the groundcover plant and arthropod assemblages within discrete patches structurally dominated by P. aquilinum or I. glabra to adjacent areas dominated by indigenous bunchgrasses. We compared local plant species richness and composition, stem density, aboveground dry biomass, and litter dry biomass, as well as arthropod species richness and composition, abundance, and dry biomass.Results Species richness and stem density of nondominant groundcover plants were significantly lower in patches of P. aquilinum and I. glabra than within bunchgrass-dominated areas. Species composition of nondominant groundcover plants was more variable within I. glabra patches compared to bunchgrass areas. Arthropod species richness and abundance were also significantly lower in patches of P. aquilinum compared to bunchgrass areas, and species composition of arthropods differed significantly between P. aquilinum patches and bunchgrass areas.Conclusions At the local scale of groundcover plant patches-along with their attendant arthropods-indigenous bunchgrasses are associated with higher species richness compared to either of the alternative foundation species P. aquilinum or I. glabra. Removal experiments, community-assembly experiments, or reciprocal replacement experiments should be conducted to test the hypothesis that these species differentially influence the groundcover as, respectively, diversity-enhancing versus diversity-inhibiting SUEs. Our observations exemplify how alternative foundation species could add complexity to natural landscapes by differentially influencing characteristics of their associated local communities.

One potential predictor of adult reproductive success is physical condition, which can be influenced by earlier developmental stages, such as nutritional limitations during juvenile growth. Sodium is a vital element for animals, essential for physiological function and individual‐level development and behaviour. When animals are sodium‐limited, they at times engage in behaviours such as cannibalism or geophagy to obtain sodium. At high levels, sodium may be toxic and result in adverse physiological effects. How dietary variation in sodium availability during larval stages influences adult mating behaviour and reproductive output has received relatively little attention. Previous studies within Lepidoptera have reported varied results. We used the bordered patch butterfly, Chlosyne lacinia (Geyer, 1837; Nymphalidae), to investigate the role of larval dietary sodium uptake on adult body size, lifespan, mating behaviour and reproductive success. Body size did not differ between treatments. Individuals raised on host plants with high‐sodium concentrations had shorter lifespans than those reared on low‐sodium host plants, indicating that sodium in high concentrations in larval diets can be harmful. Females raised on lower sodium diets took longer to start mating regardless of males' larval access to sodium, but copulation durations did not differ. Males and females raised on host plants with higher sodium concentrations mostly did not pair differently than individuals raised on host plants with lower sodium concentrations and did not differ in their immediate reproductive success. Females raised on high‐sodium host plants avoided mating with males raised on high‐sodium host treatments, suggesting that larval sodium acquisition could influence reproductive decisions made by adults. Reproductive success in insects is shaped by both intrinsic behavioural strategies and extrinsic environmental factors. During mating, individuals make complex choices to maximise fitness, and environmental conditions experienced during juvenile stages—such as dietary sodium exposure—can influence reproductive decisions in adulthood. Understanding the role of sodium in these life‐history traits is increasingly important in light of global ecological change: drought‐driven reliance on saline irrigation is accelerating soil salinisation worldwide, which may in turn disrupt insect–plant interactions and destabilise multi‐trophic dynamics. Collectively, these findings underscore how adaptive behaviours and environmental stressors interact to shape insect populations in a rapidly changing world.

Little is known about the formation, persistence, or dissolution of sleeping clusters of male bees at night roosts. We report multi-year fidelity of male Melissodes bimaculatus (Lepeletier 1825) (Hymenoptera: Apidae) sleeping clusters to a single backyard patch of irises (Iridaceae: Iris) in Baton Rouge, Louisiana. In addition, during two consecutive years, individuals (at least one male and one female) of Triepeolus lunatus (Say 1824) (Hymenoptera: Apidae) co-roosted with the male M. bimaculatus. Individual bees settled near other bees for their nocturnal rest or nighttime inactivity periods. They also appeared to sometimes bias their specific choices for roosting positions toward plant parts against which or near which their bodies were somewhat camouflaged. Thermoregulation is an unlikely ultimate evolutionary explanation for aggregated sleeping behavior in these particular bees, but protection from predators through safety in numbers and opportunities to glean information from roost mates remain as plausible adaptive explanations. We propose an extension of the Information Center Hypothesis for co-roosting by parasitic bees with their host species.

Spatial patterns of species’ distributions are often biased with respect to environmental variables, including discrete habitats. Patterns alone, however, cannot uniquely identify the combinations of processes that produced them. Many alternative processes could give rise to positive and negative habitat associations, including a population’s history of dispersal limitation and niche-based interactions with the abiotic or biotic environment, possibly owing to habitat specialization. Because of the research infrastructure and detailed species’ distributional and dynamic data provided by the 50-ha Forest Dynamics Plot, Barro Colorado Island has been a hub and catalyst for research into pat terns of local-scale habitat associations and their underlying causes. Further research into the mechanisms that generate habitat-association patterns will continue to improve our understanding of tropical community assembly, the origins and maintenance of tropical diversity, and the likely future conditions of tropical plant assemblages.

Seed size varies over more than 4 orders of magnitude among Barro Colorado Island (BCI) plants. Traits with so much interspecific variation often play important roles in trade-off-mediated coexistence, interactions with enemies and mutualists, and other community-assembly processes. Here, we focus on the 27 largest-seeded species with diaspores >5 g. These include dicots, monocots, and a gymnosperm from 14 families and 10 orders. Observations and experiments suggest that the ability to resprout after a plant suffers damage and loses tissues—either before or after germination—may be a key ultimate evolutionary explanation for the largest seed sizes. Studies on BCI were among the first to show high levels of tolerance among large-seeded species to seed infestation and damage as well as the capacity of fragments of cotyledonary tissue to differentiate a seedling axis de novo. These observations are consistent with patterns found for large seeded taxa in other tropical forests around the world.

1. Sodium is essential for animals, and its heterogeneous distribution can cause a range of phenomena, from sodium-seeking behaviours to impacting their performance. Although sodium content in soils and plants is relatively well documented, data for higher trophic levels are limited. Knowledge of the variation in sodium in lower trophic levels could have implications for understanding the behaviour and physiology of species at higher levels. 2. We investigated the variation in tissue sodium concentration between males and females of four butterfly species. Puddling behaviour of Lepidoptera suggests sodium needs of males are generally greater than females, thus, we predicted males would accumulate more sodium than females on a given diet. 3. Larvae were reared on plants (for Battus philenor, Chlosyne lacinia and Danaus plexippus) and an artificial diet (for Pieris rapae) under Low Na (no added sodium) and High Na (sodium added) conditions. Among species and sexes, we quantified and compared adult absolute tissue sodium concentrations and bioconcentration factors, which indicate net sodium accumulation or excretion relative to individuals' diets. 4. On average, individuals on low-sodium diets had higher bioconcentration values across all species. Male butterflies accumulated significantly higher sodium concentrations than females in two sodium treatments for B. philenor, and P. rapae and only in the High Na treatment for C. lacinia. However, in D. plexippus, individuals accumulate sodium in the High Na treatment, but males and females responded in the same way. 5. Our study revealed sex- and species-specific patterns of butterfly sodium accumulation, which could be linked to variations in behaviour and/or performance. Differences in sodium content across species have implications for variation in predation and trophic-level interactions, an interesting avenue for future ecological and evolutionary research.

We initiated a factorial nitrogen-phosphorus-potassium addition experiment in old-growth forest growing on an infertile Oxisol in 1998. The experiment provides clear evidence that each added nutrient limits multiple plant and ecosystem functions. All three added nutrients limit tissue nutrient concentrations, allocation to roots, and seedling growth. Phosphorus also limits soil microbial biomass, stand-level fine litter productivity, reproductive effort by trees, and soil and litter invertebrate abundance. Potassium also limits stomatal function and soil and litter invertebrate abundance. The experiment provides no evidence for diversity declines associated with eutrophication. Rather, added nutrients increased soil microbial diversity and soil and litter invertebrate diversity. Going forward, we anticipate additional lagged responses by long-lived tree species adapted to infertile soil and a shift in tree species composition to species adapted to more fertile soils. We plan further studies to explore how tropical forests maintain high productivity despite impoverished soils.

Some mistletoe species (Loranthaceae) resemble their host plants to a striking degree. Various mechanisms have been proposed for the developmental origins of novel traits that cause mistletoes to appear similar to their hosts, as well as for the adaptive phenotypic evolution of such traits. Calder (1983) proposed a logically flawed group selectionist seed-dispersal hypothesis for mistletoes to resemble their hosts. Calder's (1983) hypothesis does not provide a viable potential explanation for mistletoe resemblance to hosts.

We conducted a literature review and added some novel observations of the natural history of the bordered patch butterfly, Chlosyne lacinia (Nymphalidae). Regarding color and patterning, C. lacinia is considered one of the most variable butterflies in the Western Hemisphere, with phenotypic variation occurring in larvae, pupae, and adults. Several studies have been conducted on C. lacinia, partly due to its notable phenotypic variation and status as a pest species of domestic sunflowers (Helianthus annuus). Even so, the origins, development, and maintenance of phenotypic variation remain poorly known. Having the most extensive geographic range of any species in its genus, C. lacinia ranges from Argentina to the mid-latitude midwestern United States. Moreover, C. lacinia displays six distinct adult morphs across its geographic range. Morphologically continuous, relatively geographically narrow gradients between adjacent morphs have given rise to alternative interpretations about subspecies. By providing the first comprehensive maps of adult morphs, including data collected via citizen science in iNaturalist, we provide directions for further research into the species' biology.

As an abundant element in the Earth's crust, sodium plays an unusual role in food webs. Its availability in terrestrial environments is highly variable, but it is nonessential for most plants, yet essential for animals and most decomposers. Accordingly, sodium requirements are important drivers of various animal behavioural patterns and performance levels. To specifically test whether sodium limitation increases cannibalism in a gregarious lepidopteran herbivore, we hydroponically manipulated Helianthus annuus host plants' tissue-sodium concentrations. Gregarious larvae of the bordered patch butterfly, Chlosyne lacinia, cannibalized siblings when plant-tissue sodium concentrations were low in two separate experiments. Although cannibalism was almost non-existent when sodium concentrations were high, individual mortality rates were also high. Sodium concentration in host plants can have pronounced effects on herbivore behaviour, individual-level performance, and population demographics, all of which are important for understanding the ecology and evolution of plant-animal interactions across a heterogeneous phytochemical landscape.

Realizamos una revisión bibliográfica sobre la historia natural de la mariposa del parche bordeado, Chlosyne lacinia (Nymphalidae) que complementamos con observaciones nuevas. En cuanto al color y el patrón, C. lacinia se considera una de las mariposas más variables del hemisferio occidental, con variación fenotípica en larvas, pupas y adultos. Se han realizado numerosos estudios sobre C. lacinia, principalmente debido a su notable variación fenotípica y a su condición de especie plaga del girasol doméstico (Helianthus annuus). Aun así, el origen, desarrollo y mantenimiento de esta variación fenotípica siguen siendo poco estudiados. Teniendo la distribución geográfica más extensa de todas las especies de su género, C. lacinia se encuentra desde Argentina hasta latitudes medias del medio oeste de Estados Unidos. Además, C. lacinia presenta seis distintos morfos adultos a través de su distribución geográfica. Debido a que morfos geográficamente adyacentes presentan una morfología continua entre ellos, el reconocimiento de las subespecies es controversial. A través de mapas de distribución de cada morfo adulto con datos de iNaturalist, planteamos hipótesis y preguntas para futuras investigaciones sobre la biología de esta especie.

Plant-soil interactions can be important drivers of biological invasions. In particular, the symbiotic relationship between legumes and nitrogen-fixing soil bacteria (i.e. rhizobia) may be influential in invasion success. Legumes, including Australian acacias, have been introduced into novel ranges around the world. Our goal was to examine the acacia-rhizobia symbiosis to determine whether cointroduction of non-native mutualists plays a role in invasiveness of introduced legumes. To determine whether acacias were introduced abroad concurrently with native symbionts, we selected four species introduced to California (two invasive and two noninvasive in the region) and identified rhizobial strains associating with each species in their native and novel ranges. We amplified three genes to examine phylogenetic placement (16S rRNA) and provenance (nifD and nodC) of rhizobia associating with acacias in California and Australia. We found that all Acacia species, regardless of invasive status, are associating with rhizobia of Australian origin in their introduced ranges, indicating that concurrent acacia-rhizobia introductions have occurred for all species tested. Our results suggest that cointroduction of rhizobial symbionts may be involved in the establishment of non-native acacias in their introduced ranges, but do not contribute to the differential invasiveness of Acacia species introduced abroad.

High-diversity grasslands are increasingly recognized as “old-growth” communities, having assembled over at least millennia, and often much, much longer (1, 2). Humancaused disturbance frequently disassembles such communities, reducing them to lower-diversity states (3). A substantial challenge to conservationists interested in habitat restoration is to reassemble high-diversity communities that have been degraded by anthropogenic disturbance. Although we know that certain North American grasslands have the potential for very high diversity of plants and other organisms (1, 4), we know relatively little about the historic influences of extirpated large native herbivores, which can be keystone species in the communities they inhabit (5). Among the reasons for our ignorance are the geographic extent and nature of degradation of grassland ecosystems: Many have been extensively plowed, the natural fire regime has been altered, and large native grazers have long been absent from most (1–3, 5). In the case of native grazer removal, one of the most important unknowns is how well the effects of these missing animals can be matched by similar nonnative stand-ins. These considerations bear on broader questions in conservation biology about “rewilding” and the restoration potential of influential species of all sorts. In PNAS, Ratajczak et al. (6) share evidence that reintroduced American bison (Bison bison) more effectively diversified a Great Plains plant community—from which bison had long been extirpated—than did their nonnative counterparts, cattle. The US westward expansion of the 19th century caused bison numbers to crash and cattle numbers to soar. However, without unmodified reference sites it has been difficult to fully understand the extent to which these anthropogenic disturbances disassembled previously intact tallgrass prairie communities (5). Ratajczak et al. (6) studied the influence of native bison and domesticated cattle at the Konza Prairie Biological Station (KPBS) in Kansas, part of the Flint Hills ecoregion, which contains the largest remaining tract of unplowed tallgrass prairie (Fig. 1). For 29 y they compared vegetation among sites with bison, cattle, or neither large herbivore. During the long-term experiment, clear and consistently different trajectories characterized the three treatments. Ungrazed sites changed relatively little through time. In contrast, bison caused native plant species richness to increase compared to ungrazed sites during the nearly three-decade period, culminating in 103% higher species richness at the 10-m plot scale and 86% higher richness at the larger catchment scale (each catchment was >18 ha and sampled with 20 noncontiguous plots). At the two respective scales, cattle caused modest 41% and 30% increases in native plant species richness compared to ungrazed sites. Relatively few nonnative plants were present in any of their sites. Bison concomitantly reduced combined cover of the four dominant grass species and increased forb cover, whereas dominant grass cover in sites grazed by cattle remained at intermediate levels between the relatively low dominant grass cover with bison and the relatively high grass cover in ungrazed sites. Fire is a key process in the tallgrass prairie ecosystem (5), but prescribed fire frequency (1to 4-y return intervals) did not qualitatively change the observed outcomes with respect to grazer treatments. To foster thoughtful conservation and restoration, Aldo Leopold (7) developed the Land Ethic—his philosophy concerning humans’ responsibility toward nature. One of his metaphorical dictums was “to keep every cog and wheel is the first precaution of intelligent tinkering” (8). Even so, a general principle of community ecology is that some species play outsized roles in the ongoing process of community assembly. Keystone species wield large and disproportionately large influences relative to their abundances (9, 10). Foundation species form structurally dominant populations around which the rest of their community’s species assemble (11, 12). Ecosystem engineers create, maintain, or modify habitat by physically altering environmental materials (13). With respect to community assembly, these various species of unusual effect (SUEs) are especially important “cogs and wheels.” To remove any of these species from an intact community generally has substantial consequences for species composition, diversity, and often ecosystem function; to add one back to a community from which it was previously removed could have a similarly large effect on reversing those consequences. By increasing plant species richness relative to ungrazed sites in the Konza Prairie experiment (6), it could be argued that both bison and cattle can play keystone roles in this tallgrass ecosystem. A previous smaller-scale, shorter-term experiment at KPBS found that both bison and cattle had a diversifying influence on the prairie vegetation (14). However, within the longer-term experiment, the bison effect on native plant species richness was more than double the cattle effect at the plot scale (6). In addition, sites with bison were more resilient to extreme drought (6). During the 20 and 21 years of the study, the Konza Prairie experienced one of its most severe droughts since the Dust Bowl of the 1930s. Although the drought reversed the steady increase in species richness that had occurred before the drought in

AbstractUnderstanding the phytochemical landscapes of essential and nonessential chemical elements to plants provides an opportunity to better link biogeochemical cycles to trophic ecology. We investigated the formation and regulation of the cationic phytochemical landscapes of four key elements for biota: Ca, Mg, K, and Na. We collected aboveground tissues of plants in Atriplex, Helianthus, and Opuntia and adjacent soils from 51, 131, and 83 sites, respectively, across the southern United States. We determined the spatial variability of these cations in plants and soils. Also, we quantified the homeostasis coefficient for each cation and genus combination, by using mixed‐effect models, with spatially correlated random effects. Additionally, using random forest models, we modeled the influence of bioclimatic, soil, and spatial variables on plant cationic concentrations. Sodium variability and spatial autocorrelation were considerably greater than for Ca, Mg, or K. Calcium, Mg, and K exhibited strongly homeostatic patterns, in striking contrast to non‐homeostatic Na. Even so, climatic and soil variables explained a large proportion of plants' cationic concentrations. Essential elements (Ca, Mg, and K) appeared to be homeostatically regulated, which contrasted sharply with Na, a nonessential element for most plants. In addition, we provide evidence for the No‐Escape‐from‐Sodium hypothesis in real‐world ecosystems, indicating that plant Na concentrations tend to increase as substrate Na levels increase.

On 1 September 2020, we lost a legend in the science of ecology: Dr. Joseph (Joe) Hurd Connell, who died aged 96 (Fig. 1). Joe’s research and conceptual writings have shaped the field since the publication of his highly novel PhD study about factors controlling the abundance and vertical distribution of two barnacle species on the intertidal seashore of Scotland. His pioneering field experiments and unmatched long-term monitoring studies transformed the field of community ecology. His example moved the discipline from a predominantly descriptive endeavor of cataloging and interpreting spatial and dynamic patterns in nature to an experimental, hypothesis-driven effort aimed at understanding mechanisms responsible for these observed patterns. He also wrote several highly synthetic review papers that refocused conceptual perspectives of the discipline, constructively challenged status quo paradigms, and identified important questions for future researchers. An insatiably curious, highly creative, warmly gregarious, and wickedly funny human being, Joe enriched and forever changed the lives of hundreds of friends and scientific colleagues, not to mention literally thousands of professional ecologists and their students who studied his publications or learned about his research from the pages of every ecology textbook and many introductory biology texts. In this essay, we share and celebrate the rich history of his life and his contributions to science and its practice. Some of the personal details we include come from the invited autobiographical accounts he wrote for Current Contents in recognition of five papers that had been designated “Citation Classics” (Connell 1981, 1987, 1988, 1989, 1992) and a personal profile he wrote for Peter Stiling’s textbook, “Ecology: Theories and Applications” (Stiling 2002, pp. 118–119). These essays reveal a lot about his motivations and personal circumstances. Margaret Connell, Joe’s spouse, generously provided additional details and helped us complete the timelines. Joe’s path to an extraordinary career in ecology was far from linear and included a rich assortment of life experiences. He was born the fifth of October 1923 in Gary, Indiana, USA, and attended a Catholic elementary school in Fort Wayne, Indiana, USA. Later, his family moved to Ellwood City, outside Pittsburg, Pennsylvania, USA, where his father was employed as an engineer in the steel manufacturing industry. Joe attended high school there. In fall 1941, he enrolled at Carnegie Institute of Technology, planning on becoming an engineer like his father. However, his life changed dramatically after the attack on Pearl Harbor and the United States’ entry into WWII in December 1941. In the following year, he joined the war effort and enlisted in the US Army Air Corps in December 1942. The Air Corps had a critical need for weather forecasters, so Joe was enrolled in a specialized training program in Meteorology at the University of Chicago (1943–1944). He was then stationed in the Azores as a commissioned officer (1944–1946) with the 1st Weather Reconnaissance Squadron, serving as meteorologist on weather surveillance flights across the North Atlantic in a modified B-25D Mitchell Bomber. He gathered data essential to the safe passage of American convoys crossing the Atlantic in support of the European Theater of the war. From an early age, Joe had enjoyed watching birds and identifying trees, but growing up in a small industrial town, where most professionals he knew were medical doctors, lawyers, or engineers, he did not recognize field biology as a viable career option. However, conversations with other army enlistees, who had pursued civilian careers in biology and wildlife management before joining the war effort, convinced him that a career as a field biologist was feasible. While in the Azores, Joe hiked around the islands observing birds and other wildlife. This was where his love of natural history became an enduring part of his makeup. After the war ended, Joe returned to the University of Chicago and completed his BSc in Meteorology in 1946, but now he was determined to pursue a career in field biology. Supported by funds from the GI Bill, Joe enrolled in a master’s program in Zoology at UC Berkeley in 1947 and earned his MSc degree in 1953 under the supervision of wildlife biologist Dr. Aldo Starker Leopold. For his master’s thesis, he set out to document the movements and home range of the brush rabbit, Sylvilagus bachmani, in a chaparral-grassland-dominated canyon just east of the Berkeley campus. Leopold recommended this study organism because he thought the rabbit was abundant and a potential game animal that had been little studied. As it turned out, this proved to be dubious advice. The rabbits were very difficult to capture; over the course of his 14-month study (March 1948 to May 1949), he sampled for 2251 trap nights, but caught only 40 rabbits, and several of these became “trap-happy,” returning 6-14 times to the same trap (Connell 1954). Although his findings were an important contribution to our knowledge of brush rabbit natural history at that time, Joe found the project “frustrating” and the results “pretty dull” (Connell 1981, Stiling 2002, p. 118). This discouraging experience may explain why, after collecting his rabbit trapping data in 1948–1949, it was not until June 1953 that Joe filed his master’s thesis. (By then, he had already started, in 1952, to collect data for his doctoral dissertation!) The serendipitous consequence of this tedious rabbit project was that Joe “vowed then to adopt a simple rule of thumb, namely, never again to study anything bigger than my thumb” (Connell 1981). This pledge and a fortuitous introduction to the little-known field experimental studies of the French marine ecologist, Harry Hatton (Hatton 1938) motivated Joe’s famous study of competitive interactions between two species of barnacles on the shores of Scotland, described below. Ironically, he later immersed himself in long-term studies of corals and rainforest trees, which spend only a small fraction of their lives at a size smaller than a human thumb. Unlike brush rabbits, however, they stay put and it is relatively easy to collect data from many of them! Taking a needed break from research after his master’s work, Joe tried his hand at secondary school teaching and taught biology for two years (1949–1951) at C. K. McClatchy Senior High School in Sacramento, California, USA. Teaching was hard work, but rewarding, and he might have continued in that profession had he not received notice that he had one year left of his GI Bill funds to use immediately or lose (Stiling 2002, p. 118). Two experiences he had while in graduate school at Berkeley were pivotal in determining his next career move (Connell 1992, Stiling 2002, p. 118–119). The first was a graduate seminar he had taken as a beginning student, in which he reviewed what he described as a “wonderful” paper published in 1947 by Edward Smith Deevey (Stiling 2002, p. 118). Deevey’s paper summarized and compared the limited number of life table datasets that had been collected from natural animal populations by that time. The most complete dataset included in the review came from Hatton’s study of settlement and survival rates in multiple populations of the intertidal barnacle, Balanus (= Semibalanus) balanoides, which lived on sheltered to exposed shores adjacent to St. Malo on France’s Brittany coast (Hatton 1938). Deevey was very impressed with Hatton’s results and specifically pointed out (p. 312) that B. balanoides “is a very favorable object for population research.” Joe took note that barnacles offered many advantages over brush rabbits for quantitative experimental studies of factors controlling the distribution and abundance of natural populations (and were smaller than his thumb!). The second event that shaped the trajectory of his career was his introduction to Dr. Charles Maurice Yonge, a sabbatical visitor to Berkeley from the University of Glasgow and a renowned specialist in the physiology and morphology of marine invertebrates, especially corals, mollusks, and crustaceans. With one year of GI Bill funding in his pocket and a clear vision of the kind of research he wanted to pursue, Joe moved back across the Atlantic to pursue a PhD in Zoology with Professor Yonge. For his dissertation research (1952–1955), Joe studied barnacle populations on the shores of the Isle of Cumbrae in the Firth of Clyde, Scotland, based at the Marine Station at Millport. Because his Scottish landlady, Mrs. Plant, charged him very modest room and board (only £9 per week), he was able to stretch his one year of GI Bill funding to three (Connell 1981). This is also where, in 1952, he met Margaret Harvey, a visiting graduate student researcher from Oxford University who was studying ctenophore biology. They married in 1954 in Exeter, England, Margaret’s hometown (Fig. 2). Wanting to better understand the details of Hatton’s (1938) study, Joe painstakingly translated from French to English the entirety of Hatton’s 107-page paper, discovering that not only had Hatton gathered detailed observational data on barnacle demographics, but had used controlled field experiments to examine the factors that shaped patterns of post-settlement survival. This was a highly novel approach, perhaps the first time that such experiments had been conducted in the field under natural conditions. Prior to that time, ecological experiments had largely been relegated to the laboratory environment. Hatton scraped clean patches of the rock surface and monitored larval recruitment and subsequent survival of B. balanoides. He similarly monitored co-occurring populations of the barnacle, Chthamalus stellatus, which lives higher on the shore than B. balanoides. Hatton primarily studied the effects of density and physical factors on survival, employing controlled transplant experiments to measure the effects on survival of tidal elevation, rock surface aspect with respect to sun exposure, and an individual’s age/size. He also performed surface wetting and shading manipulations to assess the effects of heat and desiccation. Deevey’s review paper and Hatton’s research greatly inspired Joe, who always gave credit where credit was due: “my career was shifted into a new direction by Hatton and Deevey, unbeknownst to them” (Connell 1992). Since Hatton had studied the effects of physical factors in controlling barnacle distributions across the tidal gradient, Joe decided to focus on the effects of biotic interactions on the same barnacle species, initially planning to investigate predation and intraspecific competition. Professor Yonge thought this an appropriate scope for Joe’s PhD dissertation, and cautioned him not to take on too much (Connell 1981). Joe, however, had taken a field ecology course at Oxford University, taught by Charles Elton, which convinced him that competition between species was an important biotic interaction structuring natural communities. Disregarding his advisor’s counsel, Joe surreptitiously added an experimental study of interspecific competition for space between B. balanoides and C. stellatus, species that were differentially distributed along the gradient of tidal height (Connell 1961a). Amazingly, this “side study” was not included in his dissertation, but turned into probably the most widely cited and influential study that Joe conducted. Joe surmised (Connell 1981) that this study received so much attention because there was a growing body of theory about interspecific competition, but little in the way of direct experimental tests demonstrating its influence on a natural animal population. Joe felt that the central study of his dissertation (Connell 1961b), while cited less frequently, was a more substantial and better paper. The two studies are highly complementary and employed controlled manipulations of barnacle densities, transplant experiments, and predator exclusion treatments to demonstrate the impacts of competition for space and predation on density and size structure. Adult C. stellatus are most abundant on the upper shore and rare below, even though their larvae recruit over a range of lower tidal levels. Conversely, B. balanoides adults are densest at mid-shore to low shore levels and rare at upper levels, despite their larvae settling over much of the tidal range. Joe’s experiments demonstrated that, while predation by the snail, Thais (=Nucella) lapillus, reduced the density of large B. balanoides, their preferred prey, the mortality they caused was not sufficient to prevent the faster-growing B. balanoides from competitively excluding C. stellatus from the mid-shore to low shore. When B. balanoides were manually removed from the mid-shore plots, C. stellatus survived and grew well, while suffering high mortality due to competition for space with B. balanoides in unmanipulated control plots. In fact, C. stellatus grew better at mid-low shore levels, where they were more frequently submerged and filter feeding, than on the upper shore, where they were exposed to the air for longer periods. B. balanoides cannot survive the desiccating conditions characteristic of the upper shore, so the more desiccation-tolerant C. stellatus occupies this spatial refuge, free of competitive pressure from B. balanoides, thereby ensuring coexistence of the two species on the same shore. Application of these innovative yet simple experimental techniques clearly revealed the mechanisms underlying the differential distribution of species along an environmental gradient. Joe’s approach inspired the use of controlled experimentation in hundreds, if not thousands, of similar studies across a wide variety of marine, freshwater, and terrestrial habitats. In a word, Joe’s dissertation study revolutionized the science of community ecology. It is no wonder his study’s results are featured in so many introductory ecology texts. In recognition of the special significance of the work, Joe was awarded the 1963 Ecological Society of America’s Mercer Award, given for “an outstanding ecological research paper published by a younger researcher.” Joe received his PhD in Zoology from the University of Glasgow in 1956. Following a postdoctoral study at Woods Hole Oceanographic Institute (1955–1956), where he studied the spatial distribution of two species of clams, he accepted a two-year instructorship in Zoology (1956−1958) at the University of California, Santa Barbara (UCSB), and was subsequently hired as an Assistant Professor of Zoology in 1958. He spent the rest of his career at UCSB, earning tenure to Associate Professor of Zoology in 1961, and a promotion to Full Professor of Zoology in 1966. He retired in 1991 as Professor Emeritus of Zoology and held the appointment of Research Professor of Biology from 1996 to the time of his death. When he returned to the west coast of the United States, Joe sought to test the generality of the patterns he had documented in Scotland. Soon after being appointed to the faculty at UCSB, Joe headed north to the Friday Harbor Marine Laboratories on San Juan Island off the northwest coast of Washington State, where a comparable assemblage of barnacles and their snail predators occupy the intertidal zone. Working at two sites on the shore of San Juan Island, Joe conducted a series of experiments, similar to those he had used in Scotland, to study the impact of competition for space among three species of barnacles. The interactions proved quite different in this site, where three species of predatory snails (Thais spp.) preyed on the barnacles, as opposed to the single species of predatory Thais in Scotland. Their combined impact strongly reduced the density of the most common barnacle species, Balanus glandula, so that competition for space among barnacle species on the low to mid-shore was insignificant (Connell 1970), a very different outcome than Joe observed in his dissertation research. This study was among the first to demonstrate that predation can mediate the intensity of interspecific competition and thereby promote the coexistence of potentially competing prey species. The site-dependent nature of the interactions that Joe documented in Scotland versus Washington State became a major conceptual theme (i.e., context-dependence) in community ecology 40 years later. After being awarded tenure in 1961, Joe decided he “would strike out in a new research direction—try something new or outrageous—without worrying about whether it might cause a hiatus in my publication record” (Connell 1987). After studying relatively low-diversity temperate marine intertidal ecosystems for more than a decade, Joe became increasingly curious about the mechanisms that maintain high levels of species diversity in tropical ecosystems. At that time, Joe subscribed to the prevailing theory that, over evolutionary time, the high productivity and purportedly stable climatic conditions of the tropics had selected for narrow, specialized niches and high levels of species packing along resource gradients. He recognized, however, that the assumptions and predictions of this model needed to be challenged with data. By collecting long-term, spatially explicit data on demographic dynamics, including patterns of recruitment, growth, and mortality, Joe aimed to evaluate the stability of these communities and discover the mechanisms that structure them. He chose to go “all-in,” successfully applying for a Guggenheim Fellowship and moving with his family to the tropics of Australia in 1962 to study the ecological processes structuring coral assemblages on the Great Barrier Reef. During that first year in Australia, Joe met John Geoffrey Tracey and Leonard Webb of the CSIRO Rainforest Ecology Unit, the only two Australian ecologists working in rainforest at that time (Connell 1987). Their discussions gave birth to the idea of a collaborative study of mechanisms maintaining species diversity in this iconic tropical habitat, and in 1963, Joe added rainforest ecology to his portfolio. These more species-rich communities do not lend themselves as readily to the small-scale experiments that Joe had so successfully used on rocky seashores to identify the mechanisms structuring those communities. Nevertheless, he and colleagues were able to conduct manipulations of avian and mammalian seed predators and litter disturbers at his forest site in North Queensland to assess their effects on seedling assemblages (Theimer et al. 2011). The major results of his tropical work, however, come from the analysis of long-term census records collected from permanent plots established on the Great Barrier Reef and in two rainforest sites in the state of Queensland. In 1962, during his first visit to Australia, Joe established replicate permanent 1-m2 plots, line-intercept transects, and belt transects in several different sub-habitats across the reef on Heron Island near the southern end of the Great Barrier Reef. Changes in the 1-m2 plots, including the recruitment of new colonies, were quantified from 35-mm color slides taken with an SLR camera positioned vertically over each plot during 36 visits in 26 of the 38 years between 1962 and 2000 (Fig. 3; Connell et al. 1997a, 2004, Tanner et al. 2009). A year later in 1963, Joe, working with Tracey and Webb, laid out two large permanent rainforest plots, one (1.7 ha) at Davies Creek in tropical North Queensland southwest of Cairns, and the other (1.9 ha) in subtropical South Queensland near O’Reilly’s Rainforest Resort within Lamington National Park just south of Brisbane (Connell et al. 1984, Connell and Green 2000, Green et al. 2014). Seedlings and small saplings were identified, measured, and mapped within several belt transects at each location, and larger trees were individually marked and censused throughout both plots. These plots have been re-censused by teams of field assistants every few years; surviving trees are remeasured, new recruits tagged, and deaths recorded (Figs. 4-6). Through the years, literally hundreds of graduate students and postdocs "groveled" on the rainforest floor with Joe, measuring seedlings and getting leech bites as part of a ritual for aspiring field biologists. In celebration of the 50th anniversary of the establishment of these plots, Harms and Green (2014) published a description of the history and contributions of what is now known as the Connell Plots Rainforest Network. These records of community structure and dynamics may be the longest ever collected from these habitat types. Joe immediately recognized that, to make meaningful headway in studying the mechanisms maintaining diversity in these hyper-diverse communities, he needed the expertise of skilled taxonomists to accurately distinguish the many morphologically similar species co-occurring in each habitat. In addition to being accomplished ecologists, Tracey and Webb were experts at identifying rainforest plants, including their juvenile stages. Drawing on Tracey’s extensive field observations and his help compiling large sets of forest survey data, Webb had published the first physiognomic-structural classification of Australian rainforest vegetation in the Journal of Ecology in 1959. On the coral side, Dr. Carden Wallace, of James Cook University and the Museum of Tropical Queensland, provided essential help identifying corals in his plots and belt transects. Several events raised questions in Joe’s mind about the generalization that tropical communities should be considered equilibrial or “balanced” systems, tightly regulated by density or frequency-dependent biotic interactions such as interspecific competition for limited resources, predation, and disease. The first was a teatime conversation Joe had with the renowned Australian population biologist, Charles Birch, during which Joe presented his working hypothesis of stable, tightly regulated tropical communities. Birch replied: “Fine, but also keep your eyes open for tropical weather up in Queensland—some of those cyclones might shake things up a bit” (Connell 1987). The second event that challenged his assumption was in fact the impact of a severe cyclone that passed over both Heron Island and one of his rainforest plots in 1967, causing considerable damage (Connell et al. 1997a, 2004). At that time, many researchers considered these episodes rare, annoying events that “wrecked my study,” rather than drivers of community dynamics whose effects might not be recognized without long-term monitoring studies. Joe subsequently broadened his view of the possible mechanisms that could maintain diversity in these systems to include disturbance. Joe’s detailed coral and rainforest studies yielded novel insights into the processes that maintain the extraordinary levels of species diversity in these two tropical ecosystems. The studies challenged the long-standing view that these were equilibrial assemblages of tightly co-evolved species. From his 38-year record of changes in the coral system (Connell et al. 1997a, 2004, Tanner et al. 2009), Joe documented the damage caused by multiple cyclones and subsequent patterns of recovery. Large storm waves associated with these storms battered the reef, breaking and displacing colonies, while shifting sediments harmfully abraded them. Partial or complete death and displacement of colonies opened space for new recruits; competitively dominant species were knocked back and recolonization by competitively inferior species enriched the coral assemblage. This episodic reset of coral assemblages to a younger, more diverse state by disturbances of intermediate frequency and intensity as a general mechanism by which diversity is maintained is what Joe called the “Intermediate Disturbance Hypothesis” (Connell 1978). In the Queensland rainforests, a different story emerged. When storms and other natural disturbances damaged or killed trees (Connell et al. 1997b), they opened light gaps that enhanced local recruitment and growth of juvenile trees. But other diversifying processes were also at work. Joe’s good sense to study all rooted life-cycle stages of his rainforest trees arose from his earlier research, which convinced him that both the supply side and what might be called the “sorting side” (i.e., the competition, predation, disease, and habitat filtering that can non-randomly sort among individuals) were important in community ecology. The youngest seedlings on his transects clearly recruited in spatial clumps, most often near the parent tree, and recruitment rates varied year to year (e.g., Connell and Green 2000). Even so, relatively quickly the pattern diversity of cohorts of seedlings increased as they matured into later-stage saplings. These observations suggested to Joe that a combination of limited seed dispersal and the frequency-dependent influence of natural enemies—especially those that are relatively host specific—could be important diversifying mechanisms for trees (and other sessile organisms). Joe published his idea in a book chapter (Connell 1971) soon after tropical biologist Dan Janzen (1970) independently published similar thoughts. Their ideas have been linked ever since as the “Janzen-Connell Hypothesis” (Hubbell 1980). The concept has had a resounding influence on tropical forest ecology and remains one of the key elements in our collective working model for tropical rainforest diversity and dynamics (Wright 2002). Joe’s empirical findings and conceptual writings forever changed the science of ecology. With a well-deserved nod to his little-known predecessor Harry Hatton, Joe deserves credit for introducing and popularizing the use of controlled, replicated experiments to investigate ecological hypotheses in nature. One measure of the impact of his work on the discipline is how heavily his papers have been referenced by other scientists: 11 papers or book chapters have been cited over 1,000 times each. To date, these 11 papers combined have been cited 32,136 times! Joe also made major contributions to the growth of ecological theory and concepts by writing highly synthetic and critical reviews that evaluated published research results pertinent to key ecological phenomena. Especially impactful reviews addressed the role of natural enemies in preventing competitive exclusion (Connell 1971), community interactions on rocky intertidal shores (Connell 1972), shifts in species interactions along environmental gradients (Connell 1975), mechanisms of ecological succession (Connell and Slatyer 1977), hypotheses explaining the maintenance of high diversity in tropical communities (Connell 1978), the prevalence and relative importance of interspecific competition (Connell 1983), and the evidence needed to judge ecological stability and persistence (Connell and Sousa 1983). Each of these reviews has been cited more than 1,000 times to date, with the succession paper receiving more than 5,200 citations and the tropical diversity paper receiving more than 11,600! Ironically, while Joe provided perhaps the most famous demonstration that interspecific competition can shape community structure and species distributions, he also actively challenged the notion that it was the overriding and ubiquitous factor structuring communities. Several of his reviews questioned this prevailing perspective (Connell 1980, 1983) and provoked those invested in the “competition” paradigm. In the arena of applied ecology, Joe served as inaugural Chair of the Marine Review Committee (1974–1990), which was charged by the California Coastal Commission with assessment of the environmental impacts of the San Onofre Nuclear Power Plant on the coast of southern California. Joe received many honors and awards, among them two Guggenheim Fellowships, the Ecological Society’s Mercer and Eminent Ecologist awards, Fellow of The American Academy of Arts and Sciences, and corresponding member of the Australian Academy of Sciences. Joe was insatiably curious about the world around him (natural and human), and he wanted to know about everything. Few, if any, ecologists have studied as many different organisms and natural communities as Joe did, including small mammals in chaparral, rocky intertidal invertebrates, soft-sediment clams, rainforest trees, corals, and desert shrubs. He thoroughly enjoyed opportunities to immerse himself in new natural history experiences and loved engaging with students over their research ideas and results, regardless of the study organism or habitat. He was unfailingly objective about his own ideas and data, adhering to the Popperian scientific method more closely than many scientists. He did not cling to pet hypotheses; if evidence falsified one of them, he gladly moved on to consider another. Ego did not drive his scientific judgments. Joe was also highly egalitarian in his interactions with students and colleagues, especially when it came to seeking critical comments on his manuscripts. He would relentlessly pepper colleagues and students with multiple drafts of every paper he wrote. He carefully considered every comment, no matter whether it came from an undergrad or a full professor. If something was unclear, it was his fault, not the reader’s. He worked hard to clearly communicate his results and conceptual ideas in his writing, Joe gave his graduate students a lot of freedom in their choice of study organisms and field sites. He mostly cared that the questions and hypotheses were clearly stated and testable and that the findings would make a novel and valuable contribution to our understanding of the natural world. Of his 18 PhD and 2 MA thesis students, 12 worked in marine rocky intertidal habitats, two in marine soft-sediment environments, two in subtidal kelp forests, one in chaparral shrubland, one studied salmon in aquatic habitats, one studied terrestrial snails, and one studied stream flatworms. Fifteen postdoctoral researchers worked with Joe. Most collaborated on data collection, data analysis, or manuscript writing associated with either his coral reef or rainforest study. Several were involved with assessment of the potential impacts of the San Onofre Nuclear Power Plant. Others pursued their own research projects. Joe considered them peers and their collaboration greatly enhanced and expedited the analysis and publication of some of his most important research results. Joe gave detailed feedback on his students’ work. When he finished working over their papers, the bath of red ink could be visually and psychologically jarring, but the feedback always resulted in a clearer exposition of ideas. Some of his most frequent corrections were marked “No NUAs” (nouns used as adjectives) or “EUW” (eliminate unnecessary words), mixed with a few good-natured curse words. Learning to accept constructive criticism was a key part of his regimen of scientific training. He was so committed to the value of scientific data that he actually wrote up and published the dissertation chapters of two of his PhD students who were unable to do so, assigning himself second authorship. Even though he spent long hours advising on research questions and study design, he never asked to be included as an author on his students’ dissertation publications, believing that his mentoring efforts were part of his job description and that sole authorship was in the best interest of his students’ careers. It was not only the professional success of his students and colleagues that he cared about; he was also attentive to their general well-being by offering thoughtful support and kindness during hard times and, on occasion, providing practical material support for fieldwork. For example, when one of his graduate students had no means of transport to off-campus field sites, Joe donated an old, but fully functional, family car to the cause. Joe was a very social person, whether it be a campfire “billy up” at lunchtime on the side of the dirt road to the Davies Creek site (Fig. 7; https://www.nma.gov.au/exhibitions/symbols-australia/billy), or a gathering at his home to celebrate a visitor or special event. He loved hearing what people had to say, and the conversations often moved to non-scientific topics like favorite movies and books. He loved Japanese samurai films, classical music, and Marx Brothers movies, often imitating Groucho’s witty mannerisms and clever remarks. And Joe was a huge fan of the LA Dodgers. He probably cheered them to a World Series victory shortly after his own final inning in 2020. Joe is survived by his wife Margaret, their four children, Andrew, Jane, Tim, and Kate, and his niece Mary Rollins Jones, along with 11 grandchildren and seven great grandchildren. We are deeply appreciative to Joe’s family for sharing him with us; it is such a precious gift. A graduate research fund has been established in Joe’s honor at UCSB: The Joseph H. Connell Field Ecology Research Fund. Donations may be made in two ways. Those who wish to donate online can use this link: https://giving.ucsb.edu/Funds/Give?id=78 (please add "for JH Connell Fund" in the notes.). For donations by check, please make it payable to the UCSB Foundation (with “for JH Connell Fund” in the memo line) and mail to: Office of Development #2013, Attn: Bethany Innocenti, UCSB, Santa Barbara, CA 93106-2013. Questions may be directed to bethanyinnocenti@ucsb.edu. We thank Margaret Connell for providing important details about Joe’s life. We are also grateful to Betsy Mitchell for comments that improved the manuscript.

When Darwin visited the Galapagos archipelago, he observed that, in spite of the islands’ physical similarity, members of species that had dispersed to them recently were beginning to diverge from each other. He postulated that these divergences must have resulted primarily from interactions with sets of other species that had also diverged across these otherwise similar islands. By extrapolation, if Darwin is correct, such complex interactions must be driving species divergences across all ecosystems. However, many current general ecological theories that predict observed distributions of species in ecosystems do not take the details of between-species interactions into account. Here we quantify, in sixteen forest diversity plots (FDPs) worldwide, highly significant negative density-dependent (NDD) components of both conspecific and heterospecific between-tree interactions that affect the trees’ distributions, growth, recruitment, and mortality. These interactions decline smoothly in significance with increasing physical distance between trees. They also tend to decline in significance with increasing phylogenetic distance between the trees, but each FDP exhibits its own unique pattern of exceptions to this overall decline. Unique patterns of between-species interactions in ecosystems, of the general type that Darwin postulated, are likely to have contributed to the exceptions. We test the power of our null-model method by using a deliberately modified data set, and show that the method easily identifies the modifications. We examine how some of the exceptions, at the Wind River (USA) FDP, reveal new details of a known allelopathic effect of one of the Wind River gymnosperm species. Finally, we explore how similar analyses can be used to investigate details of many types of interactions in these complex ecosystems, and can provide clues to the evolution of these interactions.