Individual habitat patches may be connected by movement pathways to create habitat networks for resident organisms. Theory predicts that restrictions to movement among patches of these networks will impact population size and temporal stability at patch and network scales, but there have been few experimental tests of this prediction. We conducted laboratory experiments to explore the effect of reduced population connectivity on population outcomes in artificial habitat networks. We used populations of Daphnia carinata in replicate habitat networks of six increasingly complex topologies. With populations at dynamic equilibrium, all habitat networks were cut into two by removing the most central connections, disrupting population connectivity. The results showed that reduced population connectivity led to significantly reduced population sizes at both network and patch scales, but mainly in dendritic networks, most likely because of their topological differences. Linear and lattice networks maintained populations because they experienced minimal structural change and retained high connectivity post cut, respectively. At the patch scale, the magnitude of this decrease was significantly affected by the position of the patch within the network. The cut significantly reduced population temporal stability at network scales. Reduced habitat connectivity, causing population decline and destabilization, may lead to greater extinction risk, particularly for populations inhabiting less complex habitat networks with few inter-patch connections. Our study delivered a rare empirical test. Our results support existing conservation strategies that prioritize central dispersal pathways to reconnect habitats. By prioritizing population connectivity, managers can increase population size and stability, reducing extinction risk.
AIC (Akaike information criterion) is widely used for data analysis in ecology. Although AIC was designed to identify the better statistical model for prediction, this criterion is frequently used to identify the true relationship as a substitute for statistical tests. When an explanatory variable does not affect the response variable () in truth in generalized linear models (GLMs), the rate at which the model with the explanatory variable produces the minimal AIC was determined. This error rate is similar to the Type I error rate in hypothesis testing. When calculated numerically, the error rate was close to 0.157, which is the asymptotic value expected from the theory of the likelihood ratio test, irrespective of the link function and error structure in GLMs. Even very large sample sizes (100,000 or 1,000,000) do not prevent inflation of the error rate. The error rate increases with the number of explanatory variables when none of the explanatory variables affect in truth. Similar results were obtained in AICc, a modified form of AIC for small sample sizes. In conclusion, AIC or AICc should not be used as substitutes for statistical tests.
Understanding how invasive species populations respond to perturbations can give insight into effective management. However, opportunities to test theoretical population responses are rare, as experimental perturbations often run counter to management goals (e.g., suppression). On the island of Guam, a 5-ha outdoor enclosure (with no immigration or emigration) constructed in 2003 serves as a unique population-scale study area for invasive brown treesnakes (Boiga irregularis). Capture-mark-recapture studies (CMR) and several experiments have taken place since 2004. Here, we analyze a subset of the CMR data collected between 2008 and 2012, a time period encompassing two experimental perturbations: (1) supplemental feeding to determine if the population is food limited and (2) targeted removal of adult and large-subadult cohorts to quantify the timing and magnitude of the population's demographic response to a simulated control effort. We used the CMR data to fit a Pradel model in a Bayesian framework to compare the population growth rate, survival probability, and recruitment rate prior to, during, and post perturbations. We found that increasing food resources increased population growth and recruitment rates, but that survival remained relatively constant. The removal perturbation resulted in a decrease in population growth rate and survival immediately after the removal, but population growth rate and recruitment began increasing 1 year after the removal perturbation. Our results suggest that brown treesnakes in the enclosed population are prey limited, likely constraining population growth, and that the suppression of population growth after removal of adults and large sub-adults is short-lived (i.e., less than a year).
Herbivory, particularly by insects, significantly affects plant growth, reproduction, and survival. To cope with insect herbivory, many plants exhibit induced responses, including changes in elemental composition and the production of secondary metabolites. These responses can also occur in exotic plants that have established new interactions in the introduced regions and may vary depending on the herbivore's feeding mode. This study examines how the exotic plant Solidago altissima in Japan responds to herbivory by sap-feeding aphids (Uroleucon nigrotuberculatum) and leaf-chewing lace bugs (Corythucha marmorata). Using greenhouse experiments, we analyzed plant growth (dry mass) and quality (water, nitrogen, carbon, and phenolics) under controlled conditions. Results showed that lace bug herbivory reduced leaf dry mass by 22% and stem water content by 13%. Additionally, nitrogen content increased by 26%-81% in non-leaf organs, particularly in stems and roots. In contrast, aphid herbivory had no significant effects on plant growth or chemical composition. Regarding resource allocation, lace bug herbivory reduced nitrogen allocation to leaves by 6% while increasing allocation to stems and roots. To explain these differences, we considered three factors: (1) insect feeding modes, (2) intensity and timing of feeding damage, and (3) co-occurrence history between plants and insects. Lace bugs, which consume leaf mesophyll, likely trigger stronger plant defense responses than aphids, which feed on phloem sap and cause relatively mild stress. These findings provide insights into how exotic plants exhibit different induced and resource-allocation responses to different herbivores, particularly highlighting the strong responses of S. altissima to leaf-chewing insects like lace bugs.
Raptors, including birds of prey and owls, are apex or mesopredators that serve as vital indicators of ecosystem health. Despite their ecological importance, studies on raptor communities in tropical South Asia are scarce. This study investigates how habitat characteristics, functional traits, and dietary interactions affect raptor community structure across diverse landscapes within India. Field surveys were conducted at 445 points across seven localities, using standardized point counts within buffers of species-specific home-range sizes. Results showed that areas with increased forest height and proportion of water bodies were preferred by Brahminy kite, Lesser fish eagle, and Black-shouldered kite. Areas with increased NDVI (Normalized Difference Vegetation Index) were preferred by Spotted owlet. Deciduous broadleaf forests were often preferred by several species (e.g., Common buzzard, Eurasian kestrel and Short-toed snake eagle). Areas with increased proportion of croplands were preferred by Montagu's harrier and Black kite. The last group was clearly associated with human population (e.g., Changeable hawk eagle and Black eagle). Functional traits such as wing length, beak depth, and tarsus length were strongly linked to habitat use and foraging strategies. Community-weighted trait patterns revealed clear ecological separation among raptors across forested, wetland, and urban habitats. High dietary overlap was observed among generalist species, but spatial segregation reduced potential competition due to niche partitioning. Species with specialized diets showed minimal diet overlap, occupying distinct ecological niches. Strong correlations between dietary overlap and spatial separation were found in species-rich sites. Our findings underscore the importance of habitat heterogeneity, morphological adaptation, and spatial mechanisms in sustaining raptor diversity.
Mankyua chejuense (Ophioglossaceae) is a small, evergreen, endangered fern restricted to isolated wetlands occurring on basaltic terrain in Jeju Island, Republic of Korea. These wetlands are surrounded by evergreen broadleaf forests, but only sparse deciduous trees are found within the pools. The species' survival is strongly influenced by canopy openness and light availability, particularly during its winter growing season. This basic study aimed to identify the key factors influencing population size in M. chejuense, with a focus on genetic diversity, leaf vigor, and habitat characteristics. Using ecological data collected over a period of 2 to 10 years, we performed a path analysis to evaluate the relative influence of seven variables: population size, chloroplast DNA diversity, trophophyll and sporophyll development, photosynthetically active radiation, litter depth, and wetland area. Results showed that larger populations were associated with significantly higher genetic diversity, greater development of trophophylls and sporophylls, and occupancy of more extensive wetlands in terms of area. Such broader wetlands offered more open canopies and increased light input, particularly in winter when leaf shedding by deciduous trees enhances light penetration. In contrast, dense evergreen cover reduced light availability and was associated with lower population size and reduced reproductive frond development. These findings highlight that population viability in M. chejuense is dependent on open-canopy structures and sufficient wetland area. Conservation strategies should include limiting the expansion of evergreen broadleaf trees and maintaining open, light-accessible habitats to support long-term population persistence.
In Hokkaido, Japan, various management measures are being implemented to mitigate human-brown bear conflicts. To evaluate the effectiveness of these measures, we aimed to estimate the number of nuisance bears as an indicator of conflict based on damage and occurrence reports. For the estimation, we assessed the harmfulness level (Conditions 0-3) of the bears based on information provided in the reports and developed a method to remove duplicate or substantial overcounts of a bear resulting from multiple reports on the same individual. The specified criteria based on the difference in dates and distance were established to identify a single bear associated with multiple reports. By establishing two sets of criteria, one relaxed and one stringent, we estimated the minimum and maximum numbers of nuisance bears. We estimated the number of nuisance individuals annually based on the reports collected from 2009 to 2023 in the Oshima Peninsula, Hokkaido. The total number of nuisance individuals fluctuated between 362 and 495 (maximum) and 163 and 214 (minimum) in the first half of the 2010s. Thereafter, the maximum number of individuals in Condition 0/1 (lower harmfulness) continued to increase, reaching 504 in 2023, whereas the number of individuals in Conditions 2 and 3 remained relatively stable, ranging from 153 in 2015 to 261 in 2018. Establishing a specific criterion to estimate the number of nuisance individuals involved in conflict provides a more valuable evaluation indicator for adaptive management than one that solely relies on the number of occurrences.
Diet composition of different populations of the same raptor species may differ according to the structure of local food supply. Moreover, some prey species may be preferred more than others following raptors' prey selection. This study aimed to describe diet composition of breeding Eurasian sparrowhawks (Accipiter nisus) in relation to land cover and food supply, and to test the effect of several prey species characteristics on sparrowhawks' prey selection in a Central European rural area (Czech Republic). Data on the sparrowhawks' diet were gathered in the vicinity of their nests (a total of 1107 prey items from the surroundings of 62 nests). The structure of food supply within sparrowhawks' assumed hunting areas was estimated. Sparrowhawks' diet composition was compared with the structure of land cover and with the food supply in their hunting areas. The effect of prey species characteristics on their vulnerability to sparrowhawk predation was tested. The diet consisted almost exclusively of birds, and the diet composition was affected by the structure of land cover around the sparrowhawks' nests. Some prey species were more preferred than others. Intermediate body mass, lower population density, and brighter plumage colouration of prey species were associated with increased vulnerability to sparrowhawk predation. These results suggest that sparrowhawks specialize in hunting birds, but they can hunt a wide variety of available bird species. Their diet composition may be based on habitat structure in their hunting areas, and some prey species may be more preferred than others depending on their specific set of characteristics.
Population ecology has amassed a significant volume of demographic data across the Tree of Life. Together, these data enable comparative analyses at unprecedented taxonomic and biogeographic scales to examine patterns of demographic performance and their mechanisms. However, macroecological analysis of heterogeneous data and models from diverse study systems comes with risks, and care must be taken to ensure that the patterns from comparative approaches are biologically meaningful, rather than driven by model-specific artifacts. Recently, a balancing approach has been proposed as a solution to "distorted" population structure, particularly for evaluating transient (short-term) population dynamics. We argue that some distortion is the result of true biological processes, and that balancing over-corrects for distortion due to census timing (pre- vs. post-breeding). We lay out the relationship between demographic census design and the issues purported to be solved by balancing. Using a large dataset of carefully-selected matrix population models from plants and animals, we demonstrate that balancing changes biological interpretation of the relationship between reproductive traits and demographic resilience. We also highlight how application of balancing outside of its narrow original application to transient metrics can be problematic. We argue that meaningful comparisons require tailored approaches that respect the structure and context of demographic data. A more nuanced strategy-based on the biological realities of life cycles, census design, and reproductive strategies-will improve the robustness and interpretation of comparative demographic analyses.
The human–brown bear Ursus arctos conflicts (HBCs) have increased in Hokkaido in recent years. The recent increase in HBCs can be attributed to changes in both bear populations and human society. Brown bears in Hokkaido were added to the list of “Designated Wildlife Species for Control,” and the Hokkaido Brown Bear Management Plan (2nd period) was reviewed in 2024. The plan includes active adaptive management, zoning management, and population control, in addition to the conventional nuisance bear management and damage prevention, when the total population exceeds the region's acceptable level. HBC management should be considered as a risk management strategy for natural disasters, consisting of a combination of hazard, exposure, and vulnerability. In an adaptive management scheme, the management policy is determined every few years by each phase, based on the annual conflict and population levels for each management unit. Zoning management aims to ensure the coexistence of humans and bears through spatial segregation. When implementing management measures, land is divided into two categories: bear habitat, with deep mountain forested areas as the core habitat zone and forests around human settlements as a buffer zone; and human settlements, with rural and urban areas serving as elimination and exclusion zones, respectively. To promote brown bear management in the future, necessary measures, monitoring, and implementation systems are discussed here based on the concepts of risk management and zoning management.
Significant policy transformations in brown bear management occurred in 1963, 1990, and 2023–2024 in Hokkaido. From 1963 to 1966, the Hokkaido Government began aggressive culling of brown bears, promoting den hunting with bounties in spring (the Spring Bear-culling Program) to reduce the bear population before the occurrence of bear-caused problems. As den hunts were effective, the bear population declined, raising concerns about the possible extinction of some local populations. In 1990, the Hokkaido Government changed its policy from aggressive culling to conservation-oriented management, abolishing the Spring Bear-culling Program as the awareness of the concept of biodiversity and nature-oriented lifestyles spread. Conservation-oriented management successfully led to the recovery of the brown bear population; however, people once again faced serious conflicts and severe damage caused by bears. In response to social demands to reduce bear-caused problems, the Hokkaido Government started the Regulated Program for Spring Bear Shooting, including den hunting, in 2024 and adaptive management to maintain local populations. This history suggests that bear management in Hokkaido has fluctuated between exploitation and conservation. Generally, city residents favor conservation-oriented management, while farmers advocate for culling bears to reduce damage. Although no solution completely satisfies everyone, it is essential to develop management measures that minimize human-bear conflicts while maintaining local bear populations. Zoning-based management may provide a practical solution to reconcile polarized views. We need conservation-first zones to ensure the survival of bear populations, and bear exclusion zones to protect human lives and livelihoods. Furthermore, a community-based decision-making process should be considered when determining the zoning.
Speciation—the process by which new species arise—is fundamentally influenced by population-level factors, such as population size and demographic dynamics. Here, we review how population size and its dynamics shape speciation mechanisms and the generation of biodiversity across evolutionary scales. Small populations can undergo rapid genetic changes via drift and founder events, potentially promoting speciation, whereas large populations harbor greater genetic diversity and adaptive potential, influencing divergence in different ways. We examine how genetic drift and gene flow interact to facilitate or impede speciation under various scenarios and how extinction risk during adaptation affects the development of reproductive isolation. Finally, we explore how speciation rates and the persistence of populations/species over time are related in theoretical models. We highlight insights from mathematical models—especially those explicitly incorporating population size—and identify open questions for future research.
In many organisms, environmental temperature is a key determinant of the reproductive season, although physiological thermal responses related to reproduction often vary among taxa. Comparative analyses of reproductive seasonality within and between species can provide insights into the physiological constraints and local adaptation of reproductive traits in wild populations. This study examined wild populations of medaka (Oryzias latipes species complex). Although the photo-thermal thresholds for gonadal maturation in this species have been studied extensively in laboratory settings, geographical patterns of seasonality in gonad maturation, fecundity, and recruitment have not been thoroughly investigated in wild populations. We examined seasonal changes in gonad weight and the proportions of juveniles in wild populations of medaka at different latitudes. Our findings showed that seasonal changes in gonad weight were more pronounced in a high-latitude population in Aomori compared to a low-latitude population in Okinawa, irrespective of sex. Annual average proportions of juveniles tended to be higher in the Okinawa population compared to the Aomori and Chiba populations, suggesting a shorter recruitment period in high-latitude populations. A comparison of body size and egg number indicated that fecundity was relatively higher in high-latitude populations. We discuss whether gonad maturation at high latitudes can be explained by seasonal changes in temperature. Interpopulation differences in the gonadosomatic index and fecundity support the adaptive evolution of increased reproductive investment in high-latitude environments with shorter reproductive seasons. Additionally, trade-offs between survival and reproduction may influence ecological longevity and annual recruitment dynamics in these populations.
We propose a unified framework for constructing matrix population models in wildlife and fisheries management that accommodates variations in census timing and both natural and human-caused mortality. The approach is applicable to age-, size-, and stage-structured populations with a common short breeding season and decomposes the annual process into three components: survival (S), reproduction (B), and age increment or growth (G), each represented by a square matrix. In age-structured models, reproduction and age increment occur nearly simultaneously, but with reproduction following aging, resulting in matrix formulations such as S(BG) or (BG)S, depending on whether the census is conducted just before or after parturition. In size- or stage-structured models, where growth and survival occur in parallel, the model becomes (GS)B or B(GS), depending on the census timing. The framework also accommodates census taken at other times by partitioning survival into intervals from parturition to the census and from the census to the next parturition. Furthermore, harvest data expressed as absolute numbers can be incorporated via a capture vector structured by harvest time. This flexible modeling approach not only integrates diverse biological processes but also simplifies the construction of complex models by eliminating the need for multiple matrix formulations based on census timing, a feature often overlooked in standard textbooks on matrix population models.
The brown bear population on Hokkaido Island, once threatened, has now fully recovered. However, this recovery has led to increased conflicts with humans, including injuries and agricultural damage. In this study, we compare the effectiveness of different management strategies using indicators such as the total bear abundance and the number of nuisance bears-both of which serve as measures of extinction risk and human-wildlife conflict-by employing a population dynamics model. Additionally, we explore scenarios where the management policy is revised every 5 years, both with and without midterm revisions, based on qualitative trends in population size. Our results show that a buffer zone around urbanized areas overlaps with protected areas regardless of its width. However, a 30 km buffer would still leave 24.5% of the protected area outside the zone. Our findings suggest that under the current conditions, where population estimates are both infrequent and imprecise, and the numbers of both total and nuisance bears are high, it is challenging to mitigate conflicts without implementing population control measures. However, our results also suggest that a management approach considering both the total bear population and the number of nuisance bears can maintain low nuisance bear numbers and prevent extinction, provided mid-term policy revisions are made in response to qualitative changes in population size.
Pine wilt disease is caused by the pinewood nematode (Bursaphelenchus xylophilus Steiner et Buhrer) and induces the quick death of susceptible pine trees. In Japan, adults of the Japanese pine sawyer (Monochamus alternatus Hope) transmit the nematodes to healthy trees and oviposit on the disease-killed trees, which will produce new beetle adults with the nematodes the following year. To analyze disease epidemics, the infection models were built on an assumption of a binomial, Poisson, or negative binomial distribution of beetle visits among trees. The beetle adult density could be replaced by the mean number of emerging adults per dead tree times the density of the previous-year dead trees per unit of area. Thus, the models contained the densities of healthy and dead trees, the transmission coefficient, and a parameter whose inverse expressed the degree of aggregation of beetle visits. The models showed the stabilizing effect of highly aggregated beetle visits among trees on the incidence of pine wilt disease. In addition, those models successfully simulated the annual change in the dead tree density over 7-10 years for four Japanese red pine (Pinus densiflora Sieb. et Zucc.) stands infested with the disease and estimated the density of surviving trees at the end of the epidemic. Great positive deviations of the annual transmission coefficient values from the overall value suggested the reduced effectiveness of control measures. Discussion was made on the application of the proposed infection models to other insect-transmitted diseases of woody plants.
Space use and movement are fundamental aspects of organisms' ecology, mirroring individual fitness, behavior, and life-history strategies. These mechanisms are shaped by environmental heterogeneity, which often makes it difficult to understand these dynamics. Subterranean habitats are simplified and understudied environments, potentially ideal for evaluating the fine-scale spatial ecology of organisms. Spatial capture-recapture (SCR) methods allow us to investigate animal space use and movement, including spatially explicit observation data on individuals, to assess the relationship between population dynamics and landscape ecology. In this context, we assessed individual interactions, movement ecology, and activity patterns of a subterranean population of the cave salamander Speleomantes strinatii, applying SCR modeling to a photographic capture-recapture dataset of 104 identified individuals (43 males, 35 females and 26 subadults). Analysis of overlap indices showed that the proportion of males' home range (HR) was more covered by females' HR than vice versa (U = 25, p = 0.038). During the monitoring, females traveled longer distances in less time than males (0.60 vs. 0.22 m/day). Finally, salamanders tended to be more active during summer periods, showing a preference for the inner sectors of the cave and rougher cave walls. Combining the analysis of spatially explicit capture history (overlap and movement estimates) and SCR (activity pattern, sex-specific density and space use), we enlightened new features and confirmed previous knowledge of the spatial ecology of S. strinatii. Our study demonstrates how structured capture-recapture data can be used to infer individual interactions and movement in low-complexity habitats and is open to the application of SCR methods in more complex environments for revealing finer-scale ecological variation with important conservation implications.
The Brazilian semiarid region is characterized by high temperatures, irregular rainfall, and two distinct seasons: dry and rainy. These environmental conditions shape aquatic habitats and influence the population dynamics of freshwater organisms, reflecting adaptations to the semiarid climate. Among these organisms, two snail species stand out: the native Biomphalaria straminea (Dunker 1848), a host for the parasite causing schistosomiasis, and the invasive, parthenogenetic Melanoides tuberculata (Müller 1774), renowned for its resilience to adverse conditions. Despite their ecological and epidemiological importance, the population dynamics of these species at local and temporal scales remain poorly understood, known as the Prestonian shortfall. To address this, we conducted monthly monitoring from June 2017 to March 2020 in three reservoirs in the municipality of São Julião, Piauí, Brazil. We evaluated the dynamics of both species in response to semiarid seasonality. A total of 72,677 individuals were collected, comprising 5555 B. straminea and 67,122 M. tuberculata . B. straminea exhibited higher abundances, particularly among juveniles during the dry season, indicating sensitivity to seasonal variations. In contrast, M. tuberculata demonstrated consistent dominance throughout the year, regardless of environmental fluctuations. Analyses revealed that B. straminea was negatively impacted by the rainy season and rising temperatures, while M. tuberculata displayed remarkable tolerance and minimal seasonal adjustments. These findings underscore the enduring impact of seasonal patterns on freshwater organisms, even in artificially regulated environments such as reservoirs. They contribute to management strategies, epidemiological surveillance, and conservation efforts for aquatic biodiversity in semiarid regions.
