Ecology最新文献

Sudden habitat loss associated with environmental disturbance can trigger animals to move from affected to undisturbed areas, where increases in local density may occur. Although pathogen transmission is strongly related to local density, how crowding after habitat loss affects infection dynamics in wild populations remains unclear. Here we conceptualize the Disturbance-Density-Disease hypothesis, which posits that disturbance-induced habitat loss results in increased pathogen prevalence via increases in local density at adjacent, undisturbed patches. We then used data from before, during, and after flooding disturbance to test this hypothesis in boreal toads Anaxyrus boreas boreas co-occurring with the pathogenic fungus Batrachochytrium dendrobatidis (Bd). We collected Bd samples from captured individuals during a 5-year (2015–2019) mark-recapture study of boreal toads (n = 1295) that breed in beaver ponds in western Wyoming, USA. During spring of 2017, an extreme flooding event destroyed several beaver dams, resulting in the loss of breeding habitat. We compared host density and pathogen prevalence pre- and post-disturbance at sites affected versus unaffected by flooding. At affected sites, population density and Bd prevalence increased at adjacent, undisturbed ponds following the sudden loss of habitat. Moreover, neither host density nor Bd prevalence increased at control sites in areas unaffected by flooding. Taken together, our results support hypothesized links between disturbance, adjacent increases in density, and subsequent increases in pathogen prevalence. Our study contributes to a growing body of ecological research leveraging natural experiments to extract insights from extreme disturbance events. By doing so, we demonstrate an important consequence of disturbance beyond proximate habitat loss and introduce a clear conceptual approach (the Disturbance-Density-Disease hypothesis) to understanding how pathogen transmission can be affected by disturbance via alterations to local density.

Biological systems face multiple stressors that impact biodiversity and ecosystem functions, with complex interactions that vary spatially and temporally leading to unpredictable outcomes. In freshwater ecosystems, benthic microbial communities underpin vital functions like decomposition and primary productivity, but are threatened by stressors such as salinization and nutrient enrichment, which are intensifying and increasingly co-occurring due to climate change. We experimentally tested how stressor repetition and different orders of stressor exposure affect freshwater benthic microbial community responses over time. Communities established on tiles in 1000 L open freshwater ponds established more than 10 years ago in the field were exposed to elevated salinity and nutrient enrichment, either once or repeatedly, independently or in combination, and under different orders. Repeated exposure to nutrient enrichment led to stronger functional changes than the single exposure, while repeated exposure to elevated salinity resulted in weaker changes compared to a single exposure. Critically, we found that the sequence in which stressors occurred was a major determinant of microbial responses, driving interaction outcomes in opposing directions. When exposure to nutrient enrichment preceded elevated salinity, gross primary productivity was halved and carbon metabolic rates increased by 50% compared to communities treated in the reverse order. This study is among the first in a complex, outdoor freshwater system to demonstrate that stressor sequence can strongly shape multiple stressor effects, highlighting the order of stressor exposure as a key but often overlooked dimension of global change ecology. These findings suggest that microbial functions, including productivity and carbon cycling, will fluctuate more dramatically as stressors increasingly occur in different sequences under global change.

Sex differences are predicted to play an important role in the spread and evolution of pathogens. However, attempts to generalize the “sicker” sex have been challenged by intraspecific variability of sex biases across the infection process. Sex-specific plasticity provides a framework to resolve this by elucidating how infection is shaped at the sex-pathogen-environment interface. Using the Daphnia magna and Pasteuria ramosa system, we measure infection outcomes for males and females across three temperatures and seven pathogen densities to quantify how sex-specific plasticity shapes susceptibility, pathogen loads, and ultimately transmission. We find unique forms of plasticity at each stage of infection – including equivalent, sex-specific, and divergent plasticity. Integrating these into a single estimate of transmission reveals a clear pattern—male-biased transmission at cold temperatures, and female-biased transmission at warm temperatures. Sex-specific thermal plasticity can thus determine the “sicker” sex, with implications for pathogen spread and evolution in a warming world.

Mutualisms confer both benefits and costs to participants, but costs have been largely ignored when considering how mutualisms function and evolve. Plants that are dispersed by ants produce seeds with attached nutrient-rich food rewards (elaiosomes). When ants approach a seed, they likely assess both the benefits (elaiosome mass) and costs (mass of the inedible seed) of moving it. We hypothesized that the masses of both the seed and elaiosome would affect diaspore removal rate, and predicted that when given a choice, ants would remove diaspores with higher benefits and diaspores with lower costs more quickly. To test these hypotheses, we manipulated the elaiosomes of Datura wrightii and Datura discolor (Solanaceae) and conducted choice experiments where we presented diaspores with variable benefits and costs to colonies of the seed-dispersing ant Novomessor cockerelli (Formicidae). D. discolor has a larger elaiosome-to-seed ratio since its seeds are half the mass of D. wrightii. Consistent with our hypotheses, ants removed seeds with heavier elaiosomes (larger rewards) and lighter seeds (lower costs) more quickly. Our study provides new evidence for seed dispersal costs by quantifying a cost of seed dispersal to ants and underscores the necessity of measuring both the benefits and costs of mutualistic interactions.

More widespread species tend to be more locally abundant. This hypothesis has received support when considering single species abundance (mean density of individuals across sites) and occupancy (fraction of occupied sites) through time (intraspecific relationship) and comparing different species sampled at a single point in time (interspecific relationships). But while abundance-occupancy relationships are fairly well supported in observational studies, the underlying factors driving them are less clear. For instance, variation in demographic rates, dispersal, and spatial network structure could all influence resulting abundance-occupancy relationships. We used a simulation model to explore these relationships in spatial networks of variable size and dispersal connectivity. We simulated population dynamics on spatial networks by starting from entirely neutral communities and then systematically incorporated complexity in the form of (co)variation in species demographic rates and dispersal processes. The effect of spatial network structure on abundance-occupancy relationships was dependent on the community dynamics and the covariation imposed on demographic and dispersal parameters. Together, we demonstrate the interplay between the spatial network and variation in demographic and dispersal rates, generating testable hypotheses for when abundance-occupancy relationships would be more likely to be observed, as well as how these relationships may change with habitat fragmentation and shifts in community composition.

Plant ionomes—the suite of chemical elements making up plant tissue—constrain plant performance and the nutrition of consumers. The possible mechanisms driving Nutrient Dilution—the globally distributed decline of essential element density (parts per million [ppm]) in plant tissue—are rarely evaluated together. Toward a remedy, we explored a 30+ year record of 17 elements in the grasses, forbs, and woody plants across three burn frequencies on Konza, a North American tallgrass prairie. About one quarter of ionomic variation arose among Konza's three plant functional groups, which differed in ppm and its regulation over three decades. Nutrient-poor grass biomass increased steadily with CO₂, encroaching woody plant biomass accelerated over the same period, and nutrient-rich forb biomass decreased. Each functional group revealed its own pattern of nutrient dilution across the ionome, where it was more widespread in grasses (12/17 elements) than forbs (5/17) or woody plants (2/17). Competition with other functional groups regularly depleted the ionome ppm of grasses (9 elements) and forb and woody plants (4 elements). Unexpectedly, nutrient densities often increased in response to higher CO₂ (especially in forbs), suggesting photosynthate was invested in nutrient harvest. Fire suppression had fewer, and more idiosyncratic effects. In an era of herbivore declines, grass-feeding herbivores in this tallgrass prairie are experiencing more abundant but lower quality food. Forb feeders, in contrast, must search for less abundant but sometimes enriched food.

Poleward shifts in tropical cyclone (TC) activity have introduced unprecedented disturbances to Northeast Asia's boreal and temperate-boreal ecotone forests. As TCs migrate northward, they increasingly influence previously unaffected regions, yet their impacts on forest structure and species composition remain poorly understood. This study examines TC Maysak (2020), the most intense cyclone recorded in the ecotone forests near the Chinese–Russian border, and its effects on tree vulnerability and canopy structure. Using high-resolution drone-based orthophotographs, we analyzed fallen tree dimensions across four affected sites within protected forests, identifying key differences between coniferous and broadleaf species. Tall emergent conifers, including Manchurian fir (Abies holophylla) and Korean pine (Pinus koraiensis), were disproportionately susceptible to windthrow, with mean fallen heights exceeding the average canopy height by 4.88 ± 0.20 m (13.62 m maximally). In contrast, broadleaf species such as Mongolian oak (Quercus mongolica) exhibited minimal height variation relative to the canopy average. Our findings highlight TCs as emerging disturbance agents in Northeast Asia's temperate-boreal ecotone, preferentially removing emergent conifers, simplifying canopy structure, and promoting broadleaf dominance. As TC activity intensifies under global climate change, these disturbances may accelerate forest transitions in climatically sensitive ecotone forests.

Invasive predators can reshape native predator assemblages, triggering cascading changes in broader wildlife communities. In western North America, the barred owl (Strix varia) is an invasive apex predator with well-documented negative impacts on congeneric northern spotted owls (Strix occidentalis caurina), but impacts on other native forest owls are poorly understood. We coupled a large-scale removal experiment with a passive acoustic monitoring network to quantify species-specific and community-level responses of a five-species assemblage of native forest owls to the lethal removal of invasive barred owls. Our results supported predictions of intraguild predation theory, where smaller bodied, nocturnal species most susceptible to predation and resource competition from larger barred owls benefitted from removal, whereas a diurnally active owl species and a larger bodied species showed little to no response. We conclude that focused management actions limiting the occurrence of barred owls can provide spatial refugia for spotted owls and other sympatric native owl species, thereby promoting forest biodiversity.

Antipredator defenses typically act at distinct stages of the predation sequence—encounter, identification, approach, and subjugation. However, their effectiveness has rarely been quantified and compared simultaneously in wild predator–prey systems. We conducted a study in Peru, where we installed aviaries at two localities and recorded the responses of wild avian predators to three types of antipredator defenses—crypsis, aposematism, and evasiveness—expressed by three butterfly prey types. The study included both immature and adult birds from forest and urban environments, representing the present community of insectivorous birds. We tested the theoretical expectations that cryptic butterflies (Nymphalidae: Euptychiina) were rarely detected, aposematic Heliconius (Nymphalidae: Heliconiinae) were often sighted but seldom attacked, and evasive Spicauda (Hesperiidae: Eudaminae) were frequently detected and attacked but evaded capture at higher rates. Despite these distinct defensive strategies, mortality rates among prey types were largely similar, but predator life stage strongly influenced defense effectiveness, with immature birds tending to attack Heliconius more frequently. Additionally, predator family influenced predation patterns, with more skilled insectivores (e.g., Vireonidae) showing higher capture success against defended prey. These findings illuminate the evolutionary pressures that shape predator behavior and prey defenses in tropical ecosystems. The similar mortality rates underscore the adaptive value of these defenses, which collectively distribute the total predation pressure across prey species.