Savannas, spanning 20% of the Earth's surface, are characterized by a continuous grass matrix interspersed with woody patches, supporting high biodiversity and providing ecological and economic services. Although climatic and edaphic controls on savanna structure are well studied, the contribution of soil microbial communities in maintaining spatial heterogeneity and coexistence remains poorly understood. We investigated whether savanna heterogeneity is mirrored belowground and how disturbance and invasion by Megathyrsus maximus can modify these relationships. We used a factorial field sampling design in a mesquite savanna to compare woody patches and adjacent grasslands with and without mechanical disturbance and invasion. We quantified soil physicochemical properties, plant community composition, and bacterial and fungal communities to evaluate linkages among vegetation and soils. Grasslands and woody patches supported distinct soil and microbial assemblages, consistent with differences in vegetation inputs and nutrient regimes. Grassland microbial communities exhibited relatively simple assembly patterns, with plant diversity and soil chemistry serving as the primary correlates of community composition and stronger associations observed for fungi than bacteria. In woody patches, soil physicochemical properties were the primary correlates of microbial community composition, with plant diversity exhibiting weaker associations than in grasslands. In grasslands, invasion by M. maximus was associated with higher soil nutrient availability and shifts in microbial community composition, and mechanical disturbance correlated with similar but weaker effects. These shifts aligned with reduced grassland microbial distinctiveness and may disrupt linkages between vegetation, soils, and microbes. Aboveground patch structure in savannas aligned with belowground microbial communities and nutrient dynamics. By demonstrating that invasion and disturbance weaken these spatial patterns, this study indicates that soil microbial communities may contribute to savanna coexistence and resilience, revealing a possible association between belowground community assembly and landscape-scale heterogeneity and its destabilization under multiple stressors.

Invasive species are a leading cause of global biodiversity decline. Larvae of the cactus moth Cactoblastis cactorum Berg (Lepidoptera: Pyralidae: Phycitinae) consume prickly pear cactus species (Opuntia; Cactaceae) in its native South American range. High host specificity made C. cactorum an appropriate biological control agent of Opuntia species, which have become invasive weeds around the world. This biological control program was successful. Ironically, the success of cactus weed biological control facilitated a series of events which led to C. cactorum invasion of North America where Opuntia diversity is tremendous. In 2017, C. cactorum established along the southeast Texas coast. In 2020, we began monitoring C. cactorum dispersal towards south and south-west Texas with cactus moth pheromone traps. Our objectives were to document the extent of the invasion and calculate dispersal rates towards commercial Opuntia-growing regions in Mexico. There are four overlapping moth flight peaks in Texas. Between 2017 and 2022, the C. cactorum populations invaded over 27,000 km2 in south-east and south-central Texas at a dispersal rate up to 47 km year. Since 2022, this dispersal rate slowed as the moth invasion front came into contact with the Tamaulipan thornscrub region of south Texas where Opuntia density is high and native cactus moth species are attacked by a diverse assemblage of parasitoids. We present data on the density of native cactus moth species in Texas which shows that their density increases west and south-west of the area currently occupied by C. cactorum. These data suggest that apparent competition may be occuring between C. cactorum and native cactus moth species via shared parasitoids. This hypothesis is not mutually exclusive of other biological barriers that may contribute to explaining why the Texas C. cactorum dispersal rate has slowed significantly. We conclude with a discussion about how to leverage these data to support future deployment of C. cactorum biological control agents in Texas. Las especies invasoras son una de las principales causas del disminuci & oacute;n de la biodiversidad global. Las larvas de la polilla del cactus, Cactoblastis cactorum Berg (Lepidoptera: Pyralidae: Phycitinae) consumen especies de cactus nopal (Opuntia; Cactaceae) en su rango nativo de Sudam & eacute;rica. Alta especificidad de hu & eacute;sped hizo que C. cactorum fuera un agente de control biol & oacute;gico usado para las especies de Opuntia que fueron invasoras en todo el mundo. Este programa de control biol & oacute;gico fue exitoso. El & eacute;xito del control biol & oacute;gico de de cactus facilit & oacute; una serie de eventos que llevaron a la invasi & oacute;n de C. cactorum en Am & eacute;rica del Norte donde la diversidad de Opuntia en Am & eacute;rica del Norte es tremenda. En 2017, C. cactorum se estableci & oacute; a lado de la costa sureste de Texas. En 2020, comenzamos a monitorear la dispersi & oacute;n de C. cactorum hacia el sur y suroeste de Texas con trampas de feromonas. Nuestros objetivos eran documentar la extensi & oacute;n de la invasi & oacute;n y calcular las tasas de dispersi & oacute;n hacia las regiones comerciales de cultivo de Opuntia en M & eacute;xico. Entre 2017 y 2022, las poblaciones de C. cactorum invadieron m & aacute;s de 27,000 km2 en el sureste y centro-sur de Texas a una tasa de dispersi & oacute;n de hasta 47 km por a & ntilde;o. Desde 2022, esta tasa de dispersi & oacute;n se ha desacelerado a medida que el frente de invasi & oacute;n de la polilla entr & oacute; en contacto con la regi & oacute;n de matorral espinoso tamaulipeco del sur de Texas, donde la densidad de Opuntia es alta. Presentamos datos sobre la densidad de especies nativas de polillas del cactus en Texas que muestran que su densidad aumenta hacia el oeste y suroeste del & aacute;rea actualmente ocupada por C. cactorum. Estos datos sugieren que est & aacute; ocurriendo una competencia aparente con las especies nativas de polillas del cactus a trav & eacute;s de parasitoides compartidos. Esta hip & oacute;tesis no es excluyente de otras barreras biol & oacute;gicas que pueden a explicar por qu & eacute; la tasa de dispersi & oacute;n de C. cactorum en Texas ha disminuido. Concluimos con una discusi & oacute;n sobre c & oacute;mo aprovechar estos datos para apoyar el futuro liberaci & oacute;n de agentes de control biol & oacute;gico de C. cactorum en Texas.

We describe the wasp Iconella melitaraevora sp. nov. (Braconidae, Microgastrinae), a parasitoid of Melitara subumbrella caterpillars (Lepidoptera, Pyralidae, Phycitinae). Multiple wasp cohorts were reared from hosts collected in a montane dryland habitat of New Mexico, USA. This is the first case of gregariousness in Iconella. An updated key to American Iconella species is provided. We present a maximum likelihood tree using the cytochrome c oxidase subunit I (COI) locus of this species relative to other described Iconella species from the Americas. We also describe the biology and environmental conditions where Iconella melitaraevora sp. nov. was discovered in the context of its prickly pear cactus (Opuntia Mill.) herbivore host. The potential biological control capacity of microgastrine wasps which attack prickly pear specialist herbivores is discussed.

Novel trophic associations have sometimes resulted in fortuitous and significant biological control. After the invasion of North America by the South American cactus moth, Cactoblastis cactorum (Berg) (Pyralidae: Phycitinae), it is pertinent to characterize the assemblage of local natural enemies that could utilize this moth in new host-parasitoid associations. Herein we report on Apanteles mimoristae Muesebeck (Braconidae: Microgastrinae), a North American gregarious endoparasitoid wasp attacking the caterpillar of the phycitine cactus moth Melitara cf. nephelepasa (Dyar) (Pyralidae: Phycitinae, also known as zebra worm), also native to North America; both collected in Opuntia ficus-indica (L.) Mill. (Cactaceae) cultivated fields at rural areas of Mexico City. We provide an updated morphological account for A. mimoristae visualized with light microscopy and scanning electron microscope (SEM); a fragment of its cytochrome oxidase subunit I (COI) gene sequence data is reported for the first time. Additionally, we analyze its taxonomical position relative to other Apanteles species from the Americas including those attacking cactus-feeding moths. Our analyses place A. mimoristae (from Mexico) in a clade with A. esthercentenoae Fernández-Triana (from Costa Rica), a parasitoid of both Cromarcha stroudagnesia Solis (Pyralidae) and Palpita venatalis (Schaus) (Crambidae) (non cactus-feeding), and in a sister clade to A. opuntiarum Martínez & Berta (from Argentina) and A. alexanderi Brèthes (from Argentina and Uruguay), parasitoids of the cactus-feeding phycitines Cactoblastis and Tucumania respectively. Finally, we provide an updated key for the identification of Apanteles species recorded parasitizing cactus moth caterpillars in the American continent.

Abiotic resource limitation presents organisms with a dilemma about how to use resources when they become available. Characterizing how resource allocation affects investment in growth or defensive traits that affect organismal survival strategies allows us to understand the environmental contexts in which species interact. Our goal was to measure how macronutrient availability drives nitrogen and phosphorus allocation towards functional growth and defensive chemical traits of the Neotropical passion vine, Passiflora biflora. We investigated this question with a paired field study in La Selva, Costa Rica and a full factorial greenhouse experiment to determine whether the concentration of a key secondary chemical defence is driven by nitrogen availability. We correlated defensive chemical concentration with soil nitrogen availability in naturally occurring plants, measured the effects of nitrogen and phosphorus availability on growth and secondary chemical defence traits in the greenhouse and characterized the P. biflora leaf metabolome to assess how nutrient availability affected shifts in metabolism related to plant fitness. We found that nutrient allocation increased the magnitude of both growth and defence traits. Increased nitrogen availability resulted in higher concentrations of toxic leaf secondary chemicals, longer vines, greater biomass and more leaves with a superior ability to capture sunlight. In addition, plants from high nitrogen environments had metabolomes with significantly greater secondary metabolite richness and biochemical pathway diversity, as well as increases in the number of metabolites from several chemical classes related to basic cell function and defence. Nutrient availability had no significant effect on the richness and diversity of primary metabolites involved in basic cell functions. A direct comparison of the relative strength of quantitative growth and secondary defence traits indicated that P. biflora favours nutrient allocation to growth at low nitrogen levels but invests in both strategies more evenly as nitrogen availability increases. These findings lead us to predict that passion vines are better prepared to tolerate and resist herbivory when nutrients are plentiful and experience a trade-off between growth and chemical defence against natural enemies when they are scarce. These findings are consistent with both the 'escape' and 'defend' syndromes that are often used to describe tropical plant survival strategies. This is one of the only studies to measure nutrient allocation in vines, a group comprising a significant percentage of global plant diversity. Moreover, this work demonstrated the power of leveraging untargeted metabolomics to characterize how nutrient addition affects plant growth and defence, highlighting its potential for understanding functional trait variation.Read the free Plain Language Summary for this article on the Journal blog. La limitacion de recursos abioticos presenta a los organismos con un dilema sobre como utilizar los recursos cuando estan disponibles. Caracterizar como la asignacion de recursos afecta la inversion en rasgos de crecimiento o defensa que influyen en las estrategias de supervivencia de los organismos nos permite entender los contextos ambientales en los que interactuan las especies. Nuestro objetivo fue medir como la disponibilidad de macronutrientes afecta la asignacion de nitrogeno y fosforo hacia caracteristicas de crecimiento funcional y quimicos defensivos de la enredadera neotropical Passiflora biflora. Investigamos esta pregunta con un estudio de campo en La Reserva Biologica La Selva, Costa Rica, y un experimento de invernadero con factorial completo para determinar si la concentracion de una defensa quimica secundaria esta afectada por la disponibilidad de nitrogeno. Correlacionamos la concentracion de productos quimicos defensivos con la disponibilidad de nitrogeno en el suelo en plantas que ocurren naturalmente, medimos los efectos de la disponibilidad de nitrogeno y fosforo en el crecimiento y las caracteristicas de defensa quimica secundaria en el invernadero, y caracterizamos el metaboloma (perfil quimico total) de las hojas de P. biflora para observar como la disponibilidad de nutrientes afecto los cambios en el metabolismo relacionados con la defensa de la planta. Encontramos que la asignacion de nutrientes aumento la magnitud tanto de los caracteristicas de crecimiento como de defensa. Una mayor disponibilidad de nitrogeno resulto en concentraciones mas altas de productos quimicos secundarios toxicos en las hojas, en endredederas mas largas, mayor masa y hojas con una capacidad superior para capturar la luz solar. Ademas, las plantas crecidas con alto contenido de nitrogeno tenian metabolomas con una riqueza de metabolitos secundarios significativamente mayor y una mayor diversidad de vias bioquimicas, asi como un aumento en el numero de metabolitos de varias clases quimicas relacionadas con la funcion celular basica y la defensa. La disponibilidad de nutrientes no tuvo un efecto significativo en la riqueza y diversidad de metabolitos primarios involucrados en funciones celulares basicas. Una comparacion directa de la fuerza relativa de los caracteristicas de crecimiento y defensa secundaria indico que P. biflora prefiere la asignacion de nutrientes al crecimiento en niveles bajos de nitrogeno, pero invierte en ambas estrategias de manera mas igual a medida que aumenta la disponibilidad de nitrogeno. Estos resultados nos llevan a predecir que las Passiflora estan mejor preparadas para tolerar y resistir el herbivorismo cuando los nutrientes son abundantes, y tienen un intercambio entre el crecimiento y la defensa quimica contra los enemigos naturales cuando los nutrients son pobres. Estos resultados son consistentes tanto con los sindromes de 'escape' y 'defence' que muchos utilizan para describir las estrategias de supervivencia de las plantas tropicales. Este es uno de los pocos estudios que miden la asignacion de nutrientes en enredaderas, un grupo que tiene un porcentaje grande de la diversidad vegetal global. Ademas, este trabajo demostro el poder de aprovechar la metabolomica para caracterizar como la adicion de nutrientes afecta el crecimiento y la defensa de las plantas, mostrando su potencial para entender la variacion en los caracteristicas funcionales. Read the free Plain Language Summary for this article on the Journal blog.image

Plants host diverse assemblages of fungi on their foliar tissues, both in internal compartments and on exterior surfaces. When plant distributions shift, they can move with their fungal associates (i.e., co-introduction) or acquire new associates present in the novel environment (host-jumping). The fungal communities that plants acquire influence a plant's ability to establish and spread in this new environment. Here, we aimed to assess whether invasive C. ciliaris hosts similar groups of fungi in its native and introduced ranges and to evaluate community overlap of fungi associated with foliar tissue of C. ciliaris and native and non-native plants within the introduced range. In the introduced range, the majority of OTUs associated with C. ciliaris were not found in its native range, although 3.2% of OTUs were common to both ranges. Of these shared OTU, 77.6% were found on co-occurring natives and non-natives in the introduced range, whereas 22.4% were unique to C. ciliaris indicating a possible co-introduction. Fungal communities within the introduced range contained a higher proportion of generalist symbionts and increased heterogeneity of foliar communities than in its native range. Within the introduced range, host phylogenetic distance explained more variation than native status. Our findings provide evidence that non-natives acquire fungi opportunistically from their environment, although host and environmental filtering is present suggesting that successful invasive plants may be able to limit the effect of poor symbionts and select for better ones. Future experimental work will be needed to confirm the occurrence of host selection and identify its mechanisms.

A collection of egg parasitoids in the Scelionidae are identified as members of the Telenomus californicus Ashmead, 1893 complex (californicus+dalmanni+arzamae groups). They were reared from eggs of the cactus zebra worm, Melitara cf. junctoliniella Hulst, 1900 (Pyralidae: Phycitinae) infesting Opuntia streptacantha Lemaire, 1839 (Cactaceae) at Bustamante, Nuevo León, Mexico. Lacking both male specimens and a revision of the complex, no species-level identification could be made. The taxonomic placement of these wasps is discussed as well as possible implementation of these egg parasitoids in new-association biological control of the invasive cactus moth Cactoblastis cactorum (Berg, 1885) (Pyralidae: Phycitinae) in North America.

Wide-ranging species are subject to varying biotic and abiotic selection pressures across their distribution. While local adaptation does not manifest in obvious morphological changes, population genomic studies can reveal cryptic diversity and provide insights into local adaptive processes. In this study, we investigated the biogeographic history and genomic diversity across the range of the zebra longwing butterfly Heliconius charithonia, a species with a widespread distribution in the Neotropics, but which is phenotypically homogenous across its range. We examined whole genome sequence data from 55 individuals from the eight described subspecies. We infer that there were at least two distinct colonization events of the Caribbean islands from the mainland. The second colonization wave occurred relatively recently, accounting for the genetic homogeneity observed across the species' range. Despite low divergence across most of the genome, two large non-recombining genomic regions showed deeply divergent haplotypes that correspond to chromosomal inversions. Phylogenetic analyses indicate ancient origins of these inversion polymorphisms, and there is no evidence that they were introgressed from another extant lineage of Heliconius. These ancient polymorphisms are likely maintained by heterogeneous selection across the landscape, with the inversion on chromosome 19 likely playing a role in local adaptation to cold and desiccation. Our findings underscore the importance of genomic analysis in uncovering hidden diversity and adaptation in phenotypically homogenous species and highlight the significant role of chromosomal inversions in driving local adaptation. ### Competing Interest Statement The authors have declared no competing interest.

Invasive grasses cause devastating losses to biodiversity and ecosystem function directly and indirectly by altering ecosystem processes. Escape from natural enemies, plant-plant competition, and variable resource availability provide frameworks for understanding invasion. However, we lack a clear understanding of how natural stressors interact in their native range to regulate invasiveness. In this study, we reduced diverse guilds of natural enemies and plant competitors of the highly invasive buffelgrass across a precipitation gradient throughout major climatic shifts in Laikipia, Kenya. To do this, we used a long-term ungulate exclosure experiment design across a precipitation gradient with nested treatments that (1) reduced plant competition through clipping, (2) reduced insects through systemic insecticide, and (3) reduced fungal associates through fungicide application. Additionally, we measured the interaction of ungulates on two stem-boring insect species feeding on buffelgrass. Finally, we measured a multiyear smut fungus outbreak. Our findings suggest that buffelgrass exhibits invasive qualities when released from a diverse group of natural stressors in its native range. We show natural enemies interact with precipitation to alter buffelgrass productivity patterns. In addition, interspecific plant competition decreased the basal area of buffelgrass, suggesting that biotic resistance mediates buffelgrass dominance in the home range. Surprisingly, systemic insecticides and fungicides did not impact buffelgrass production or reproduction, perhaps because other guilds filled the niche space in these highly diverse systems. For example, in the absence of ungulates, we showed an increase in host-specific stem-galling insects, where these insects compensated for reduced ungulate use. Finally, we documented a smut outbreak in 2020 and 2021, corresponding to highly variable precipitation patterns caused by a shifting Indian Ocean Dipole. In conclusion, we observed how reducing natural enemies and competitors and certain interactions increased properties related to buffelgrass invasiveness.

Hox gene clusters encode transcription factors that drive regional specialization during animal development: for example the Hox factor Ubx is expressed in the insect metathoracic (T3) wing appendages and differentiates them from T2 mesothoracic identities. Hox transcriptional regulation requires silencing activities that prevent spurious activation and regulatory crosstalks in the wrong tissues, but this has seldom been studied in insects other than Drosophila , which shows a derived Hox dislocation into two genomic clusters that disjoined Antennapedia ( Antp ) and Ultrabithorax ( Ubx ). Here, we investigated how Ubx is restricted to the hindwing in butterflies, amidst a contiguous Hox cluster. By analysing Hi-C and ATAC-seq data in the butterfly Junonia coenia , we show that a Topologically Associated Domain (TAD) maintains a hindwing-enriched profile of chromatin opening around Ubx . This TAD is bordered by a Boundary Element (BE) that separates it from a region of joined wing activity around the Antp locus. CRISPR mutational perturbation of this BE releases ectopic Ubx expression in forewings, inducing homeotic clones with hindwing identities. Further mutational interrogation of two non-coding RNA encoding regions and one putative cis- regulatory module within the Ubx TAD cause rare homeotic transformations in both directions, indicating the presence of both activating and repressing chromatin features. We also describe a series of spontaneous forewing homeotic phenotypes obtained in Heliconius butterflies, and discuss their possible mutational basis. By leveraging the extensive wing specialization found in butterflies, our initial exploration of Ubx regulation demonstrates the existence of silencing and insulating sequences that prevent its spurious expression in forewings.

Invasive species are the second largest contributor to biodiversity loss and drivers of ecosystem change. Buffelgrass is a C4, perennial grass native to Africa and Asia that was widely introduced across tropical and subtropical rangelands as livestock forage. Buffelgrass reduces native biodiversity and ecosystem stability in its introduced range when it escapes livestock pastures. Understanding the ecology of insects associated with buffelgrass in its native range may provide an understanding of invasion processes and biological control opportunities where buffelgrass has become an invasive challenge. Here, we present the results of a six-year survey of herbivorous arthropods of a native buffelgrass population from Kenya. Buffelgrass was examined for externally and internally feeding insects of vegetative and reproductive tissues. We also categorised buffelgrass detritivores and parasitoids that may use buffelgrass herbivores as hosts. The samples were photographed and Sanger sequenced to identify them to the lowest possible taxonomic ranking. We collected information on sample abundances, phenologies, tissues consumed, and putative diet breadths. We identified 25 morphospecies representing seven orders and 16 families. The putative host plant specialisation was as high as 67% for Diptera. Phenological variation in herbivore presence correlated with seasonal rainfall and provided a guide for when to conduct follow-up biological control agent searches. The most abundant herbivore was a gall midge (Diptera: Cecidomyiidae) that inhabits buffelgrass culms. Additional research should focus on bringing this species into containment where host choice trials can be conducted to determine if it is truly monophagous and assess its impact on buffelgrass growth.

Host plant specialisation by herbivorous insects is ubiquitous, especially among the Lepidoptera. Many taxa have the ability to accumulate toxic compounds from their host plants that serve as chemical defences against natural enemies. Despite common knowledge of this pattern among insect ecologists, we still have much to learn about how dietary variation affects an insect's ability to acquire toxic plant chemicals. Longwing butterfly larvae (Heliconius) accumulate toxic cyanogenic glucosides from their host plants, passion vines (Passiflora), that make them toxic to most predators. Here, we present on zebra longwing (H. charithonia) caterpillar cohorts that were reared on native P. affinis, P. biflora, P. lutea, or P. suberosa to determine how host usage affected cyanide accumulation over larval developmental stages, and ultimately the toxicity of adult butterflies. Samples were collected at third, fourth and fifth instars, and teneral adults. Cyanogenic glucosides were extracted, the cyanide molecules were captured as sodium cyanide (CN), and CN content was quantified colorimetrically. The quantity of CN acquired increased linearly over larval ontogeny and was variable among host plants. CN concentration increased over larval development for two hosts but declined on the third. There was no clear relationship between host plant and adult CN concentrations, but adults that consumed certain hosts as larvae ended up accumulating significantly more CN, and thus expressed higher CN concentrations, than others. We demonstrated that some host plants provide specialist insects with more toxins than others and that larval secondary chemical accumulation may predict which life stages are more vulnerable to natural enemies. These conclusions support the hypothesis that host choice affects the survival of specialist insect herbivores.

The acquisition of novel sexually dimorphic traits poses an evolutionary puzzle: How do new traits arise and become sex-limited? Recently acquired color vision, sexually dimorphic in animals like primates and butterflies, presents a compelling model for understanding how traits become sex-biased. For example, some Heliconius butterflies uniquely possess UV (ultraviolet) color vision, which correlates with the expression of two differentially tuned UV-sensitive rhodopsins, UVRh1 and UVRh2. To discover how such traits become sexually dimorphic, we studied Heliconius charithonia, which exhibits female-specific UVRh1 expression. We demonstrate that females, but not males, discriminate different UV wavelengths. Through whole-genome shotgun sequencing and assembly of the H. charithonia genome, we discovered that UVRh1 is present on the W chromosome, making it obligately female-specific. By knocking out UVRh1, we show that UVRh1 protein expression is absent in mutant female eye tissue, as in wild-type male eyes. A PCR survey of UVRh1 sex-linkage across the genus shows that species with female-specific UVRh1 expression lack UVRh1 gDNA in males. Thus, acquisition of sex linkage is sufficient to achieve female-specific expression of UVRh1, though this does not preclude other mechanisms, like cis-regulatory evolution from also contributing. Moreover, both this event, and mutations leading to differential UV opsin sensitivity, occurred early in the history of Heliconius. These results suggest a path for acquiring sexual dimorphism distinct from existing mechanistic models. We propose a model where gene traffic to heterosomes (the W or the Y) genetically partitions a trait by sex before a phenotype shifts (spectral tuning of UV sensitivity).

Biological invasions are a leading ecological issue of the 21st century because of their worldwide contributions to biodiversity loss and degradation of ecosystem services. Answering general questions about the mechanisms facilitating the spread of successful invasives is key to understanding how to manage them moving forward. The success of introduced primary producers has often been attributed to superior competitive ability or to their release from natural enemies that constrained them in their native range. In contrast, nonnative primary producers can successfully invade and establish in new areas by releasing allelochemical compounds into the environment that are toxic to the native flora. The interactive effects of allelopathy and competition remain underexplored. Here, we evaluated the mechanism of invasion by Guinea grass, a globally distributed tallgrass from tropical and subtropical Africa with known allelopathic effects associated with 2-hydroxyphenylacetic acid (2HPAA). We asked if allelopathy and light availability interact to give Guinea grass a competitive advantage during seedling establishment in its introduced range. We used a fully factorial greenhouse experiment in which allelochemical concentrations and light availability treatments were based on empirical measurements of these variables at an invaded site in South Texas. Seedling recruitment and growth were assessed for three native species and for Guinea grass itself. We also described the metabolome (the complete set of small molecules) of an invasive grass for the first time to facilitate a comparison of the effect of the known allelochemical 2HPAA with that of the whole-plant chemical extract. Shading and allelochemistry each reduced recruitment and growth by themselves, and a significant interaction of these stressors exacerbated the negative effects in the shade, resulting in short plants, low biomass, and ultimately decreased seedling recruitment. The whole-plant metabolomic extract had significantly stronger effects than pure 2HPAA, and these negative effects were intensified in the shade. Moreover, the mechanism showcased here demonstrated that resource competition and biochemical interference are not mutually exclusive mechanisms that facilitate the spread of a globally distributed invasive species.

The potential for targeted grazing for restoration through the removal of invasive species represents an effective tool for practitioners. This study examines the impact of targeted grazing across highly variable precipitation on buffelgrass, a widely introduced African grass that often escapes cultivation. We simulated targeted grazing, overgrazing, and no grazing by clipping at two intensities and not clipping in a third treatment. We did this in plots with buffelgrass invasion and documented buffelgrass size and reproduction, as well as native plant community diversity. Additionally, as a further proxy for grazing, we tracked root allocation by buffelgrass in mowed and unmowed plots for 25 months while documenting large variability in precipitation. We found that targeted grazing reduced the negative impact of buffelgrass on the native community; on the other hand, overgrazing reduced the native community diversity. Precipitation interacted with simulated grazing such that buffelgrass subjected to grazing was less tolerant to drought and future simulated herbivory after rains returned. Long‐term targeted grazing may lead to reductions in buffelgrass that allow the restoration of the native plant community, which benefits the biodiversity of flora and fauna, and supports multiple uses of rangelands.

Plant-soil feedback (PSF) processes play an integral role in structuring plant communities. In native grass-lands, PSF has a largely negative or stabilizing effect on plant growth contributing to species coexistence and succession, but perturbations to a system can alter PSF, leading to long-term changes. Through chang-es to soil abiotic and biotic properties, invasion by non-native plants has a strong impact on belowground processes with broad shifts in historical PSFs. Guinea grass, Megathyrsus maximus, an emerging invasive in South Texas, can efficiently exclude native plants in part due to its fast growth rate and high biomass accumulation, but its impacts on belowground processes are unknown. Here, we provide a first look at PSF processes in South Texas savannas currently undergoing invasion by Guinea grass. In this pilot study, we addressed the question of how the presence of the invasive M. maximus may alter PSF compared to uninvaded grasslands. Under greenhouse conditions, we assessed germination and growth of Guinea grass and the seed bank in soil collected from grasslands invaded and uninvaded by Guinea grass. We found that Guinea grass grown in soil from invaded grasslands grew taller and accumulated higher biomass than in soil from uninvaded grasslands. Plants grown from the seed bank were more species rich and abundant in soil from uninvaded grasslands but had higher biomass in soil from invaded grasslands. In South Texas savan-nas, we found evidence to support shifts in the direction of PSF processes in the presence of Guinea grass with positive feedback processes appearing to reinforce invasion and negative feedback processes possibly contributing to species coexistence in uninvaded grasslands. Future work is needed to determine the mech-anisms behind the observed shifts in PSF and further explore the role PSF has in Guinea grass invasion.

A significant challenge of global change is the human-mediated movement of pasture grasses and their subsequent impact on ecosystem processes when they become invasive. We must understand invasive grass ecology and their natural enemies in native and introduced ranges to mitigate these impacts. Guinea grass (Megathyrsus maximus) is a pantropically introduced pasture grass that escapes intended areas and invades native ecosystems – threatening biodiversity and ecosystem function. The success of invasive plants has often been attributed to ecological release from stressors, including natural enemies and resource availability. Our objective was to assess Guinea grass functional traits across three different habitat types in native and invaded ranges by documenting ungulate and arthropod abundance, diversity, and feeding guilds. Guinea grass functional traits were assessed in three habitat types: grassland, riparian, and woody thickets around nitrogen-fixing Prosopis glandulosa in its introduced range in Texas, USA, and Senegalia mellifera in its native range in Kenya. We characterized Guinea grass functional traits by measuring plant height, cover, biomass, root-to-shoot ratios, and reproductive traits. We then examined the phytophagous arthropod and ungulate abundance and feeding guild diversity across the three habitat types. We hypothesized that functional trait expression related to invasiveness would be associated with Guinea grass in its introduced range. Also, we hypothesized that the abundance and diversity of phytophagous arthropods and ungulates would be lower in the invaded range. Finally, we hypothesized that Guinea grass functional traits would differ between the three habitat types, given the habitat types’ innate differences in resource availability. We found that Guinea grass was 2.5 times taller and 3.3 times more productive and covered 2.5 times more area in its invaded versus native ranges. Introduced Guinea grass had higher reproduction rates with 2.5 times more reproductive tillers, while habitat type drove vegetative reproduction with 15 times more stoloniferous establishment in wooded and riparian sites than grasslands. Texan ungulate communities were less species-rich, less functionally diverse, and less abundant than the Kenyan ungulate community. The phytophagous arthropod diversity on plants was twice as high on Kenyan Guinea grass than on Texan Guinea grass. Total arthropod family richness was nearly double, with 15 families represented in Kenya and 8 in Texas. These results suggest that Guinea grass has escaped a rich assemblage of arthropods and ungulates and likely explains some of its spread in introduced ranges. This study demonstrates how the invasive success of Guinea grass can be understood in terms of its competitive ability and interaction with natural enemies in the introduced and native ranges and may inform future biological control.

Non-native grass invasion is a leading driver of biodiversity loss and degradation of rangeland ecosystem services. The reproductive mode and output of alien species mediate invasion, and their differential propagule pressure has implications for management outcomes. Propagule success, however, is context dependent. Resource availability promotes invasion and is heavily influenced by disturbance regimes. This study measured the reproductive phenology and establishment of Guinea grass's vegetative and seed-based reproduction in the field and the greenhouse. We asked how differences in vegetation type (woodland vs. grassland), disturbance history (brush management), and their interaction mediate the invasion process of Guinea grass. We documented differences in reproductive phenology as a function of vegetation type and disturbance history in the field. We measured seedling emergence and establishment in the greenhouse by fully crossing environmental variables with soils from two different disturbance levels. Finally, we estimated propagule pressure across vegetation types and disturbance history using data collected from the field and greenhouse trials. We found that areas associated with higher soil nutrients (under nitrogen-fixing mesquite trees and soil disturbance) had higher seed and stolon propagule pressure. Conversely, low disturbance and grassland areas had lower propagule pressure and were associated with lower nutrients. In the greenhouse, seedling establishment interacted with vegetation and disturbance. Seedlings growing in soils from mottes in a high-disturbance pasture had higher biomass and shoot length. However, the low disturbance pasture's specific root length was highest in mottes, indicating a higher allocation to roots, investing toward resource capture. Subsequently, we posit a hypothesis for Guinea grass spread in South Texas. Our findings suggest potential management steps, including treating Guinea grass under wooded cover to reduce overall propagule pressure and minimize soil disturbance during brush management of partially invaded woodlands. (C) 2022 The Society for Range Management. Published by Elsevier Inc. All rights reserved.