Sex and occupation time influence niche space of a recovering keystone predator

Rechsteiner, Erin U.; Watson, Jane C.; Tinker, M. Tim; Nichol, Linda M.; Henderson, Matthew J. Morgan; McMillan, Christie J.; DeRoos, Mike; Fournier, Marie C.; Salomon, Anne K.; Honka, Leah D.; Darimont, Chris T.

doi:10.1002/ece3.4953

Cited by 17 publications

(14 citation statements)

References 55 publications

(152 reference statements)

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“…Although θ > 1 is a reasonable assumption for most long‐lived cetaceans and pinnipeds (Taylor and Demaster 1993), our fitted model for southern sea otters actually suggests a value of θ slightly below 1 (Table 1; although the 95% CrI for θ includes 1). The lower value of θ for sea otters implies that density‐dependent effects on reproduction and survival emerge soon after population establishment, a pattern supported by empirical data from several recovering populations (Bodkin et al 2000, Rechsteiner et al 2019, Tinker et al 2019 a ). Regardless, the reason that our candidate value of OSP is >0.5 K is not indicative of a convex functional form of density‐dependent growth but rather reflects the incorporation of parameter uncertainty in our estimates of K and MNPL.…”

Section: Discussionmentioning

confidence: 76%

Habitat Features Predict Carrying Capacity of a Recovering Marine Carnivore

et al. 2021

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The recovery of large carnivore species from over‐exploitation can have socioecological effects; thus, reliable estimates of potential abundance and distribution represent a valuable tool for developing management objectives and recovery criteria. For sea otters (Enhydra lutris), as with many apex predators, equilibrium abundance is not constant across space but rather varies as a function of local habitat quality and resource dynamics, thereby complicating the extrapolation of carrying capacity (K) from one location to another. To overcome this challenge, we developed a state‐space model of density‐dependent population dynamics in southern sea otters (E. l. nereis), in which K is estimated as a continuously varying function of a suite of physical, biotic, and oceanographic variables, all described at fine spatial scales. We used a theta‐logistic process model that included environmental stochasticity and allowed for density‐independent mortality associated with shark bites. We used Bayesian methods to fit the model to time series of survey data, augmented by auxiliary data on cause of death in stranded otters. Our model results showed that the expected density at K for a given area can be predicted based on local bathymetry (depth and distance from shore), benthic substrate composition (rocky vs. soft sediments), presence of kelp canopy, net primary productivity, and whether or not the area is inside an estuary. In addition to density‐dependent reductions in growth, increased levels of shark‐bite mortality over the last decade have also acted to limit population expansion. We used the functional relationships between habitat variables and equilibrium density to project estimated values of K for the entire historical range of southern sea otters in California, USA, accounting for spatial variation in habitat quality. Our results suggest that California could eventually support 17,226 otters (95% CrI = 9,739–30,087). We also used the fitted model to compute candidate values of optimal sustainable population abundance (OSP) for all of California and for regions within California. We employed a simulation‐based approach to determine the abundance associated with the maximum net productivity level (MNPL) and propose that the upper quartile of the distribution of MNPL estimates (accounting for parameter uncertainty) represents an appropriate threshold value for OSP. Based on this analysis, we suggest a candidate value for OSP (for all of California) of 10,236, which represents 59.4% of projected K. © 2021 The Authors. The Journal of Wildlife Management published by Wiley Periodicals LLC on behalf of The Wildlife Society.

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Section: Discussionmentioning

confidence: 76%

Habitat Features Predict Carrying Capacity of a Recovering Marine Carnivore

et al. 2021

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“…At the broadest level, our understanding of this trophic cascade is based on the presence/absence of sea otters (Enhydra lutris) in an ecosystem, linked to human exploitation patterns associated with the maritime fur trade and subsequent repatriation patterns in the North Pacific [4]. More recent work has illustrated the effect of sea otters on kelp forest community structure via space-for-time comparisons of locations differing in the duration of otter occupancy post re-introductions [5][6][7]. While this conceptual framework includes human impacts on the ecosystem via intensive harvesting or reintroduction of otters, it does not adequately capture the more nuanced role humans can play in the ecosystem where otters and humans co-occur and interact.…”

Section: Introductionmentioning

confidence: 99%

Southeast Alaskan kelp forests: inferences of process from large-scale patterns of variation in space and time

et al. 2022

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Humans were considered external drivers in much foundational ecological research. A recognition that humans are embedded in the complex interaction networks we study can provide new insight into our ecological paradigms. Here, we use time-series data spanning three decades to explore the effects of human harvesting on otter–urchin–kelp trophic cascades in southeast Alaska. These effects were inferred from variation in sea urchin and kelp abundance following the post fur trade repatriation of otters and a subsequent localized reduction of otters by human harvest in one location. In an example of a classic trophic cascade, otter repatriation was followed by a 99% reduction in urchin biomass density and a greater than 99% increase in kelp density region wide. Recent spatially concentrated harvesting of otters was associated with a localized 70% decline in otter abundance in one location, with urchins increasing and kelps declining in accordance with the spatial pattern of otter occupancy within that region. While the otter–urchin–kelp trophic cascade has been associated with alternative community states at the regional scale, this research highlights how small-scale variability in otter occupancy, ostensibly due to spatial variability in harvesting or the risk landscape for otters, can result in within-region patchiness in these community states.

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“…Perhaps less documented, and rarely considered a key marine subsidy vector, is the terrestrial activity of sea otters Enhydra lutris . While they are often described as the keystone predator that specializes in red sea urchins Mesocentrotus franciscanus , observational studies indicate that they will switch to clams, other bivalves and crustaceans once urchin populations are depleted, especially when large sea otter colonies occupy soft‐sediment habitats (Kvitek et al , Rechsteiner et al ). In certain instances, the clam species Tresus nuttallii and Saxidomus nuttalli can comprise over half of the prey harvested from nearshore habitats (Kvitek et al ).…”

Section: Vectors Of Shellfish Transfer Into Terrestrial Systemsmentioning

confidence: 99%

Shellfish subsidies along the Pacific coast of North America

et al. 2020

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Spatial subsidies are associated with pronounced ecosystem responses, as nutrients cross ecological boundaries and cascade through food webs. While the importance of subsidies is known, the role of shellfish, specifically molluscs, as a marine subsidy has not been formally described. Focusing primarily on the Pacific coast of North America, we identify vectors that transport shellfish-derived nutrients into coastal terrestrial environments, including birds, mammals, and over 13 000 yr of marine resource use by people. Evidence from recipient ecosystems suggests shellfish drastically influence soil chemistry, forest productivity and the diversity of primary producers at the regional and landscape level. Responses in higher trophic levels have not yet been investigated, but given documented responses in lower trophic levels, this may be due to a lack of examination. To determine if the processes we describe within the northeast Pacific are pertinent to coastal environments worldwide, we also explore shellfish subsidies globally, with a specific focus on temperate and tropical islands. As shellfish are not as spatially or temporally constrained as other subsidies, our examination suggests our findings are applicable to many other geographical regions along the marine-terrestrial interface. Marine subsidiesMarine subsidies occur when nutrients are transferred from marine to terrestrial ecosystems, anywhere along the 594 000 km of global coastline (Hammond 1990). These subsidies can take the form of seabird guano (Sánchez-Piñero and Polis 2000), marine mammal carcasses (Polis and Hurd 1996), spawning fishes (Fox et al. 2015, Reimchen 2018 or macroalgae deposition (Spiller et al. 2010). While all of these subsidies play important roles in shaping terrestrial productivity, their effect sizes vary over space and time. For example, relatively brief, intense pulses of marine nutrients are deposited in riparian forests during annual Pacific salmon Oncorhynchus spp. autumn spawning (Gende et al.

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Sex and occupation time influence niche space of a recovering keystone predator

Cited by 17 publications

References 55 publications

Habitat Features Predict Carrying Capacity of a Recovering Marine Carnivore

Habitat Features Predict Carrying Capacity of a Recovering Marine Carnivore

Southeast Alaskan kelp forests: inferences of process from large-scale patterns of variation in space and time

Shellfish subsidies along the Pacific coast of North America

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