Project description:Manipulative parasites that promote their transmission by altering their host's phenotype are widespread in nature, which suggests that host manipulation allows the permanent coexistence of the host with the parasite. However, the underlying mechanism by which host manipulation affects community stability remains unelucidated. Here, using a mathematical model, we show that host manipulation can stabilise community dynamics. We consider systems wherein parasites are transmitted between different trophic levels: intermediate host prey and final host predator. Without host manipulation, the non-manipulative parasite can destabilise an otherwise globally stable prey-predator system, causing population cycles. However, host manipulation can dampen such population cycles, particularly when the manipulation is strong. This finding suggests that host manipulation is a consequence of self-organized behavior of the parasite populations that allows permanent coexistence with the hosts and plays a key role in community stability.
Project description:The predator discrimination of prey can affect predation intensity and the prey density dependence of predators, which has the potential to alter the coexistence of prey species. We used a predator-prey population dynamics model accounting for the predator's adaptive diet choice and predator discrimination of prey to investigate how the latter influences prey coexistence. The model revealed that (i) prey species that are perceived as belonging to the same species by a predator are attacked in the same manner, and it is more difficult for them to coexist than those that are recognized as different prey species, and (ii) prey species that are not discriminated by a predator-and therefore cannot coexist-may coexist in the presence of an alternative predator that does discriminate between them. These results suggest that prey diversity, which favours the predator discrimination of prey, and the different capabilities of predators to identify prey species both enhance prey coexistence.
Project description:The geographic mosaic theory of coevolution predicts 1) spatial variation in predatory structures as well as prey defensive traits, and 2) trait matching in some areas and trait mismatching in others mediated by gene flow. We examined gene flow and documented spatial variation in crushing resistance in the freshwater snails Mexipyrgus churinceanus, Mexithauma quadripaludium, Nymphophilus minckleyi, and its relationship to the relative frequency of the crushing morphotype in the trophically polymorphic fish Herichthys minckleyi. Crushing resistance and the frequency of the crushing morphotype did show spatial variation among 11 naturally replicated communities in the Cuatro Ciénegas valley in Mexico where these species are all endemic. The variation in crushing resistance among populations was not explained by geographic proximity or by genetic similarity in any species. We detected clear phylogeographic patterns and limited gene flow for the snails but not for the fish. Gene flow among snail populations in Cuatro Ciénegas could explain the mosaic of local divergence in shell strength and be preventing the fixation of the crushing morphotype in Herichthys minckleyi. Finally, consistent with trait matching across the mosaic, the frequency of the fish morphotype was negatively correlated with shell crushing resistance likely reflecting the relative disadvantage of the crushing morphotype in communities where the snails exhibit relatively high crushing resistance.
Project description:Eco-evolutionary frameworks can explain certain features of communities in which ecological and evolutionary processes occur over comparable timescales. Here, we investigate whether an evolutionary dynamics may interact with the spatial structure of a prey-predator community in which both species show limited mobility and predator perceptual ranges are subject to natural selection. In these conditions, our results unveil an eco-evolutionary feedback between species spatial mixing and predators perceptual range: different levels of mixing select for different perceptual ranges, which in turn reshape the spatial distribution of prey and its interaction with predators. This emergent pattern of interspecific interactions feeds back to the efficiency of the various perceptual ranges, thus selecting for new ones. Finally, since prey-predator mixing is the key factor that regulates the intensity of predation, we explore the community-level implications of such feedback and show that it controls both coexistence times and species extinction probabilities.
Project description:Cannibalism among predators is a key intraspecific interaction affecting their density and foraging behavior, eventually modifying the strength of predation on heterospecific prey. Interestingly, previous studies showed that cannibalism among predators can increase or reduce predation on heterospecific prey; however, we know less about the factors that lead to these outcomes. Using a simple pond community consisting of Hynobius retardatus salamander larvae and their associated prey, I report empirical evidence that cannibalism among predators can increase predation on large heterospecific prey but reduce that on small heterospecific prey. In a field-enclosure experiment in which I manipulated the occurrence of salamander cannibalism, I found that salamander cannibalism increased predation on frog tadpoles but reduced that on aquatic insects simultaneously. The contrasting effects are most likely to be explained by prey body size. In the study system, frog tadpoles were too large for non-cannibal salamanders to consume, while aquatic insects were within the non-cannibals' consumable prey size range. However, when cannibalism occurred, a few individuals that succeeded in cannibalizing reached large enough size to consume frog tadpoles. Consequently, although cannibalism among salamanders reduced their density, salamander cannibalism increased predation on large prey frog tadpoles. Meanwhile, salamander cannibalism reduced predation on small prey aquatic insects probably because of a density reduction of non-cannibals primarily consuming aquatic insects. Body size is often correlated with various ecological traits, for instance, diet width, consumption, and excretion rates, and is thus considered a good indicator of species' effects on ecosystem function. All this considered, cannibalism among predators could eventually affect ecosystem function by shifting the size composition of the prey community.
Project description:Predation is one of the key ecological mechanisms allowing species coexistence and influencing biological diversity. However, ecological processes are subject to contemporary evolutionary change, and the degree to which predation affects diversity ultimately depends on the interplay between evolution and ecology. Furthermore, ecological interactions that influence species coexistence can be altered by reciprocal coevolution especially in the case of antagonistic interactions such as predation or parasitism. Here we used an experimental evolution approach to test for the role of initial trait variation in the prey population and coevolutionary history of the predator in the ecological dynamics of a two-species bacterial community predated by a ciliate. We found that initial trait variation both at the bacterial and ciliate level enhanced species coexistence, and that subsequent trait evolutionary trajectories depended on the initial genetic diversity present in the population. Our findings provide further support to the notion that the ecology-centric view of diversity maintenance must be reinvestigated in light of recent findings in the field of eco-evolutionary dynamics.
Project description:Stable isotope analyses, particularly of carbon (δ13C) and nitrogen (δ15N), are used to investigate ecological relationships among species. For marine predators, research has shown the main factors influencing their intra-specific and intra-individual isotopic variation are geographical movements and changes in the composition of diet over time. However, as the differences seen may be the result of changes in the prey items consumed, a change in feeding location or the combination of both, knowledge of the temporal and spatial consistency in the isotopic values of prey becomes crucial for making accurate inferences about predator diets. This study used an abundant marine predator, the Australasian gannet (Morus serrator), as prey sampler to investigate the annual variation in fish and squid prey isotope values over a four-year period (2012-2015) and the geographic variation between two sites with contrasting oceanographic conditions. Significant inter-annual variation was observed in δ13C and/or δ15N values of five of the eight prey species analysed. The strongest inter-annual variation in both δ13C and δ15N values occurred in 2015, which coincided with a strong El Niño-Southern Oscillation (ENSO). This may suggest a temporal fluctuation in the geographic source of prey or the origin of their nutrients. These results suggest that it is important to consider the potential significant differences in isotopic values within the prey assemblages that predators consume. This is important to improve the interpretation of marine predator isotope results when determining the influence of environmental variability on their diets.
Project description:Predator-prey interaction is inherently spatial because animals move through landscapes to search for and consume food resources and to avoid being consumed by other species. The spatial nature of species interactions necessitates integrating spatial processes into food web theory and evaluating how predators combine to impact their prey. Here, we present a spatial modeling approach that examines emergent multiple predator effects on prey within landscapes. The modeling is inspired by the habitat domain concept derived from empirical synthesis of spatial movement and interactions studies. Because these principles are motivated by synthesis of short-term experiments, it remains uncertain whether spatial contingency principles hold in dynamical systems. We address this uncertainty by formulating dynamical systems models, guided by core habitat domain principles, to examine long-term multiple predator-prey spatial dynamics. To describe habitat domains, we use classical niche concepts describing resource utilization distributions, and assume species interactions emerge from the degree of overlap between species. The analytical results generally align with those from empirical synthesis and present a theoretical framework capable of demonstrating multiple predator effects that does not depend on the small spatial or temporal scales typical of mesocosm experiments, and help bridge between empirical experiments and long-term dynamics in natural systems.
Project description:The outcome of species interactions may manifest differently at different spatial scales; therefore, our interpretation of observed interactions will depend on the scale at which observations are made. For example, in ladybeetle-aphid systems, the results from small-scale cage experiments usually cannot be extrapolated to landscape-scale field observations. To understand how ladybeetle-aphid interactions change across spatial scales, we evaluated predator-prey interactions in an experimental system. The experimental habitat consisted of 81 potted plants and was manipulated to facilitate analysis across four spatial scales. We also simulated a spatially explicit metacommunity model parallel to the experiment. In the experiment, we found that the negative effect of ladybeetles on aphids decreased with increasing spatial scales. This pattern can be explained by ladybeetles strongly suppressing aphids at small scales, but not colonizing distant patches fast enough to suppress aphids at larger scales. In the experiment, the positive effects of aphids on ladybeetles were strongest at three-plant scale. In a model scenario where predators did not have demographic dynamics, we found, consistent with the experiment, that both the effects of ladybeetles on aphids and the effects of aphids on ladybeetles decreased with increasing spatial scales. These patterns suggest that dispersal was the primary cause of ladybeetle population dynamics in our experiment: aphids increased ladybeetle numbers at smaller scales because ladybeetles stayed in a patch longer and performed area-restricted searches after encountering aphids; these behaviors did not affect ladybeetle numbers at larger spatial scales. The parallel experimental and model results illustrate how predator-prey interactions can change across spatial scales, suggesting that our interpretation of observed predator-prey dynamics would differ if observations were made at different scales. This study demonstrates how studying ecological interactions at a range of scales can help link the results of small-scale ecological experiments to landscape-scale ecological problems.
Project description:Simian foamy viruses (SFV) are ancient retroviruses of primates and have coevolved with their host species for as many as 30 million years. Although humans are not naturally infected with foamy virus, infection is occasionally acquired through interspecies transmission from nonhuman primates. We show that interspecies transmissions occur in a natural hunter-prey system, i.e., between wild chimpanzees and colobus monkeys, both of which harbor their own species-specific strains of SFV. Chimpanzees infected with chimpanzee SFV strains were shown to be coinfected with SFV from colobus monkeys, indicating that apes are susceptible to SFV superinfection, including highly divergent strains from other primate species.