1,721,131 research outputs found
The persistence of populations facing climate shifts and harvest
No full textMany species are expected to shift their geographic distribution as climates change, and yet climate change is only one of a suite of stressors that species face. Species that might, in theory, be able to shift rapidly enough to keep up with climate velocity (the rate and direction that isotherms move across the landscape) may not in actuality be able to do so when facing the cumulative impacts of multiple stressors. Despite empirical reports of substantial interactions between climate change and other stressors, we often lack a mechanistic understanding of these interactions. Here, we developed and analyzed a spatial population dynamics model to explore the cumulative impacts of climate with another dominant stressor in the ocean and on land: harvest. We found that critical rates of climate velocity and harvest depend on the growth rate and dispersal kernel of the population, as well as the magnitude of the other stressor. This allowed us to identify conditions under which harvesting and climate velocity can together drive populations extinct even when neither stressor would do so in isolation. Except in these extreme cases, we also found that the interaction between the declines in biomass caused by climate velocity and harvest is approximately additive. Finally, we have shown that threshold harvest rules can be effective management tools to mitigate the interaction between the two stressors, while protected areas can either help or hinder,depending on how harvesters reallocate their effort. We also have parameterized the model for black rockfish (Sebastes melanops) to demonstrate the model’s broad applicability.Received 22 December 2014; revised 25 February 2015; accepted 4 March 2015; final version received 8 May 2015; published 23 September 2015.Peer reviewe
Diversity in thermal affinity among key piscivores buffersimpacts of ocean warming on predator–prey interactions
No full textAsymmetries in responses to climate change have the potential to alter importantpredator–prey interactions, in part by altering the location and size of spatial refugiafor prey. We evaluated the effect of ocean warming on interactions between fourimportant piscivores and four of their prey in the U.S. Northeast Shelf by examiningspecies overlap under historical conditions (1968–2014) and with a doubling in CO2.Because both predator and prey shift their distributions in response to changingocean conditions, the net impact of warming or cooling on predator–prey interac-tions was not determined a priori from the range extent of either predator or preyalone. For Atlantic cod, an historically dominant piscivore in the region, we foundthat both historical and future warming led to a decline in the proportion of preyspecies’ range it occupied and caused a potential reduction in its ability to exerttop-down control on these prey. In contrast, the potential for overlap of spiny dog-fish with prey species was enhanced by warming, expanding their importance aspredators in this system. In sum, the decline in the ecological role for cod thatbegan with overfishing in this ecosystem will likely be exacerbated by warming, butthis loss may be counteracted by the rise in dominance of other piscivores withcontrasting thermal preferences. Functional diversity in thermal affinity within thepiscivore guild may therefore buffer against the impact of warming on marineecosystems, suggesting a novel mechanism by which diversity confers resilience.Peer reviewe
Response of marine communities to local temperature changes
No full textAs global climate change and variability drive shifts in species’ distributions, ecological communities are being reorganized. One approach to understand community change in response to climate change has been to characterize communities by a collective thermal preference, or community temperature index (CTI), and then to compare changes in CTI with changes in temperature. However, important questions remain about whether and how responsive communities are to changes in their local thermal environments. We used CTI to analyze changes in 160 marine assemblages (fish and invertebrates) across the rapidly-changing Northeast U.S. Continental Shelf Large Marine Ecosystem and calculated expected community change based on historical relationships between species presence and temperature from a separate training dataset. We then compared interannual and long-term temperature changes with expected community responses and observed community responses over both temporal scales. For these marine communities, we found that community composition as well as composition changes through time could be explained by species associations with bottom temperature. Individual species had non-linear responses to changes in temperature, and these nonlinearities scaled up to a nonlinear relationship between CTI and temperature. On average, CTI increased by 0.36°C (95% CI: 0.34–0.38°C) for every 1°C increase in bottom temperature, but the relationship between CTI and temperature also depended on community composition. In addition, communities responded more strongly to interannual variation than to long-term trends in temperature. We recommend that future research into climate-driven community change accounts for nonlinear responses and examines ecological responses across a range of temporal and geographical scales.Peer reviewe
Path-dependent institutions drive alternative stable states in conservation
No full textUnderstanding why some renewable resources are overharvested while others are conserved remains an important challenge. Most explanations focus on institutional or ecological differences among resources. Here, we provide theoretical and empirical evidence that conservation and overharvest can be alternative stable states within the same exclusive-resource management system because of path- dependent processes, including slow institutional adaptation. Sur- prisingly, this theory predicts that the alternative states of strong conservation or overharvest are most likely for resources that were previously thought to be easily conserved under optimal manage- ment or even open access. Quantitative analyses of harvest rates from 217 intensely managed fisheries supports the predictions. Fisheries’ harvest rates also showed transient dynamics characteris- tic of path dependence, as well as convergence to the alternative stable state after unexpected transitions. This statistical evidence for path dependence differs from previous empirical support that was based largely on case studies, experiments, and distributional anal- yses. Alternative stable states in conservation appear likely out- comes for many cooperatively managed renewable resources, which implies that achieving conservation outcomes hinges on har- nessing existing policy tools to navigate transitions.Peer reviewe
Model-based inference for estimating shifts in species distribution, area occupied and centre of gravity
No full text1. Changing climate is already impacting the spatial distribution of many taxa, including bees, plants, birds, butterflies and fishes. A common goal is to detect range shifts in response to climate change, including changes in the centre of the population’s distribution (the centre of gravity, COG), population boundaries and area occupied. Conventional estimators, such as the abundance-weighted average (AWA) estimator for COG, confound range shifts with changes in the spatial distribution of available survey data and may be biased when the distribution of survey data shifts over time. AWA also does not estimate the standard error of COG in individual years and cannot incorporate data from multiple survey designs.
2. To explicitly account for changes in the spatial distribution of survey effort, we propose an alternative species distribution function (SDF) estimator. The SDF approach involves calculating distribution metrics, including COG, population boundary and area occupied, directly from the predicted species distribution or density function. We illustrate the SDF approach using a spatio-temporal model that is available as an R package. Using simulated data, we confirm that the SDF substantially decreases bias in COG estimates relative to the AWA estimator. We then illustrate the method by analysing data from two data sets spanning 1977–2013 for 18 marine fishes along the U.S. West Coast.
3. In our case study, the SDF estimator shows significant northward shifts for six of 18 species (with southward shifts for only 2), where two species (darkblotched and greenstriped rockfishes) have both a northward shift and a decreased area occupied. Pelagic species (e.g. Pacific hake and spiny dogfish) have more variable distribution than bottom-associated species. We also find substantial differences between AWA and SDF estimates of COG that are likely caused by shifts in sampling distribution (which affect the AWA but not the SDF estimator).
4. We caution that common estimators for range shift can yield inappropriate inference whenever sampling designs have shifted over time. We conclude by suggesting further improvements in model-based approaches to analysing climate impacts, including methods addressing the impact of local and regional temperature changes on species distribution.Peer reviewe
Greater vulnerability to warming of marine versus terrestrial ectotherms
No full textUnderstanding which species and ecosystems will be most severely affected by warming as climate change advances is important for guiding conservation and management. Both marine and terrestrial fauna have been affected by warming1,2 but an explicit comparison of physiological sensitivity between the marine and terrestrial realms has been lacking. Assessing how close populations live to their upper thermal limits has been challenging, in part because extreme temperatures frequently drive demographic responses3,4 and yet fauna can use local thermal refugia to avoid extremes5–7. Here we show that marine ectotherms experience hourly body temperatures that are closer to their upper thermal limits than do terrestrial ectotherms across all latitudes—but that this is the case only if terrestrial species can access thermal refugia. Although not a direct prediction of population decline, this thermal safety margin provides an index of the physiological stress caused by warming. On land, the smallest thermal safety margins were found for species at mid-latitudes where the hottest hourly body temperatures occurred; by contrast, the marine species with the smallest thermal safety margins were found near the equator. We also found that local extirpations related to warming have been twice as common in the ocean as on land, which is consistent with the smaller thermal safety margins at sea. Our results suggest that different processes will exacerbate thermal vulnerability across these two realms. Higher sensitivities to warming and faster rates of colonization in the marine realm suggest that extirpations will be more frequent and species turnover faster in the ocean. By contrast, terrestrial species appear to be more vulnerable to loss of access to thermal refugia, which would make habitat fragmentation and changes in land use critical drivers of species loss on land.Peer reviewe
Genomic signatures of environmental selection despite near-panmixia in summer flounder
No full textRapid environmental change is altering the selective pressures experienced by marine species. While adaptation to local environmental conditions depends on a balance between dispersal and natural selection across the seascape, the spatial scale of adaptation and the relative importance of mechanisms maintaining adaptation in the ocean are not well understood. Here, using population assignment tests, Approximate Bayesian Computation (ABC), and genome scans with double-digest restriction-site associated DNA sequencing data, we evaluated population structure and locus--environment associations in a commercially important species, summer flounder (Paralichthys dentatus), along the U.S. east coast. Based on 1,137 single nucleotide polymorphisms across 232 individuals spanning nearly 1,900 km, we found no indication of population structure across Cape Hatteras, North Carolina (FST = 0.0014) or of isolation by distance along the coast using individual relatedness. ABC estimated the probability of dispersal across the biogeographic break at Cape Hatteras to be high (95% credible interval: 7%--50% migration). However, we found 15 loci whose allele frequencies were associated with at least one of four environmental variables. Of those, 11 were correlated with bottom temperature. For summer flounder, our results suggest continued fisheries management as a single population and identify likely response mechanisms to climate change. Broadly speaking, our findings suggest that spatial balancing selection can manifest in adaptive divergence on regional scales in marine fish despite high dispersal, and that these conditions likely result in the widespread distribution of adaptive alleles and a high potential for future genetic adaptation in response to changing environmental conditions. In the context of a rapidly changing world, a landscape genomics perspective offers a useful approach for understanding the causes and consequences of genetic differentiation.Peer reviewe
Who Should Pick the Winners of Climate Change?
No full textMany conservation strategies identify a narrow subset of genotypes, species, or geographic locations that are predicted to be favored under different scenarios of future climate change. However, a focus on predicted winners, which might not prove to be correct, risks undervaluing the balance of biological diversity from which climate-change winners could otherwise emerge. Drawing on ecology, evolutionary biology, and portfolio theory, we propose a conservation approach designed to promote adaptation that is less dependent on uncertain predictions about the identity of winners and losers. By designing actions to facilitate numerous opportunities for selection across biological and environmental conditions, we can allow nature to pick the winners and increase the probability that ecosystems continue to provide services to humans and other species.Peer reviewe
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