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Abstract Keystone predation can be a determinant of community structure, including species diversity, but factors underlying “keystoneness” have been minimally explored. Using the system in which the original keystone, the sea starPisaster ochraceus, was discovered, we focused on two potential (but overlapping) determinants of keystoneness: intrinsic traits or state variables of the species (e.g., size, density), and extrinsic environmental parameters (e.g., prey productivity) that may provide conditions favorable for keystone predator evolution. Using a comparative‐experimental approach, with repeated field experiments at multiple sites across a variable coastal environment, we tested predation rates, or how quickly predators consumed prey, and predation effects, or community response to predator presence or absence. We tested five hypotheses: (H1) predation rates and effects will vary in space but not time; (H2) per population predation rates will vary primarily with individual traits and population variables; (HJHH3) per capita predation rates will vary only with individual traits; (H4) predation effects will vary with traits, variables, and external drivers; and (H5) as predicted by the keystone predation hypothesis, diversity will vary unimodally with predation pressure. As hypothesized, predation rates differed among sites but not over time (H1), and in caging exclusion experiments, predation effect varied with both intrinsic and extrinsic factors (H4). Unexpectedly, predation rates varied with both intrinsic and extrinsic (H2, per population), or only with extrinsic (H3, per capita) factors. Further, in large‐plot exclusion experiments, predation effect was most closely associated with individual traits (contraH4). Finally, taxon diversity varied unimodally with proxies of predation pressure (sessile prey abundance) and was sensitive to extrinsic factors (mussel growth, temperature, and upwelling,H5). Hence, keystoneness depended on predator individual traits, predator population variables, and environmental parameters. However, temporal differences in caging experiments suggested that environmental characteristics underlying prey dynamics may be preeminent. Compared to prior experiments, predation was weaker with low prey input compared to periods with high prey input. Collectively, our results suggest that keystone predator evolution depends on the coalescence of species‐specific characteristics, and environmental parameters favoring high prey productivity. Our approach may be a model for future studies exploring the generality of keystoneness.
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The far-reaching effects of genetic process in a keystone predator species, grey wolves
Although detrimental genetic processes are known to adversely affect the viability of populations, little is known about how detrimental genetic processes in a keystone species can affect the functioning of ecosystems. Here, we assessed how changes in the genetic characteristics of a keystone predator, grey wolves, affected the ecosystem of Isle Royale National Park over two decades. Changes in the genetic characteristic of the wolf population associated with a genetic rescue event, followed by high levels of inbreeding, led to a rise and then fall in predation rates on moose, the primary prey of wolves and dominant mammalian herbivore in this system. Those changes in predation rate led to large fluctuations in moose abundance, which in turn affected browse rates on balsam fir, the dominant forage for moose during winter and an important boreal forest species. Thus, forest dynamics can be traced back to changes in the genetic characteristics of a predator population.
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- Award ID(s):
- 1939399
- PAR ID:
- 10479410
- Publisher / Repository:
- Science
- Date Published:
- Journal Name:
- Science Advances
- Volume:
- 9
- Issue:
- 34
- ISSN:
- 2375-2548
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract Landscapes of fear can determine the dynamics of entire ecosystems. In response to perceived predation risk, prey can show physiological, behavioral, or morphological trait changes to avoid predation. This in turn can indirectly affect other species by modifying species interactions (e.g., altered feeding), with knock‐on effects, such as trophic cascades, on the wider ecosystem. While such indirect effects stemming from the fear of predation have received extensive attention for herbivore–plant and predator–prey interactions, much less is known about how they alter parasite–host interactions and wildlife diseases. In this synthesis, we present a conceptual framework for how predation risk—as perceived by organisms that serve as hosts—can affect parasite–host interactions, with implications for infectious disease dynamics. By basing our approach on recent conceptual advances with respect to predation risk effects, we aim to expand this general framework to include parasite–host interactions and diseases. We further identify pathways through which parasite–host interactions can be affected, for example, through altered parasite avoidance behavior or tolerance of hosts to infections, and discuss the wider relevance of predation risk for parasite and host populations, including heuristic projections to population‐level dynamics. Finally, we highlight the current unknowns, specifically the quantitative links from individual‐level processes to population dynamics and community structure, and emphasize approaches to address these knowledge gaps.more » « less
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Abstract Invasive predatory species are frequently observed to cause evolutionary responses in prey phenotypes, which in turn may lead to evolutionary shifts in the population dynamics of prey. Research has provided a link between rates of predation and the evolution of prey population growth in the lab, but studies from natural populations are rare. Here, we tested for evolutionary changes in population dynamics parameters of zooplanktonDaphnia pulicariafollowing invasion by the predatorBythotrephes longimanusinto Lake Kegonsa, Wisconsin, US. We used a resurrection ecological approach, whereby clones from pre‐ and post‐invasive periods were hatched from eggs obtained in sediment cores and were used in a 3‐month growth experiment. Based on these data, we estimated intrinsic population growth rates (r), the shape of density dependence (θ) and carrying capacities (K) using theta‐logistic models. We found that post‐invasionDaphniamaintained a higherrandKunder these controlled, predation‐free laboratory conditions. Evidence for changes inθwas weaker. Whereas previous experimental evolution studies of predator–prey interactions have demonstrated that genotypes that have evolved under predation have inferior competitive ability when the predator is absent, this was not the case for theDaphnia. Given that our study was conducted in a laboratory environment and the possibility for genotype‐by‐environment interactions, extrapolating these apparent counterintuitive results to the wild should be done with caution. However, barring such complications, we discuss how selection for reduced predator exposure, either temporally or spatially, may have led to the observed changes. This scenario suggests that complexities in ecological interactions represents a challenge when predicting the evolutionary responses of population dynamics to changes in predation pressure in natural systems.more » « less
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Nielsen, Rasmus (Ed.)Abstract Island ecosystems provide natural laboratories to assess the impacts of isolation on population persistence. However, most studies of persistence have focused on a single species, without comparisons to other organisms they interact with in the ecosystem. The case study of moose and gray wolves on Isle Royale allows for a direct contrast of genetic variation in isolated populations that have experienced dramatically differing population trajectories over the past decade. Whereas the Isle Royale wolf population recently declined nearly to extinction due to severe inbreeding depression, the moose population has thrived and continues to persist, despite having low genetic diversity and being isolated for ∼120 years. Here, we examine the patterns of genomic variation underlying the continued persistence of the Isle Royale moose population. We document high levels of inbreeding in the population, roughly as high as the wolf population at the time of its decline. However, inbreeding in the moose population manifests in the form of intermediate-length runs of homozygosity suggestive of historical inbreeding and purging, contrasting with the long runs of homozygosity observed in the smaller wolf population. Using simulations, we confirm that substantial purging has likely occurred in the moose population. However, we also document notable increases in genetic load, which could eventually threaten population viability over the long term. Overall, our results demonstrate a complex relationship between inbreeding, genetic diversity, and population viability that highlights the use of genomic datasets and computational simulation tools for understanding the factors enabling persistence in isolated populations.more » « less
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- Free Publicly Accessible Full Text
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Accepted Manuscript1.0
- Journal Article:
- https://doi.org/10.1126/sciadv.adc8724
