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A dispersal-induced paradox: synchrony and stability in stochastic metapopulations
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Understanding how dispersal influences the dynamics of spatially distributed populations is a major priority of both basic and applied ecologists. Two well-known effects of dispersal are spatial synchrony (positively correlated population dynamics at different points in space) and dispersal-induced stability (the phenomenon whereby populations have simpler or less extinction-prone dynamics when they are linked by dispersal than when they are isolated). Although both these effects of dispersal should occur simultaneously, they have primarily been studied separately. Herein, I summarise evidence from the literature that these effects are expected to interact, and I use a series of models to characterise that interaction. In particular, I explore the observation that although dispersal can promote both synchrony and stability singly, it is widely held that synchrony paradoxically prevents dispersal-induced stability. I show here that in many realistic scenarios, dispersal is expected to promote both synchrony and stability at once despite this apparent destabilising influence of synchrony. This work demonstrates that studying the spatial and temporal impacts of dispersal together will be vital for the conservation and management of the many communities for which human activities are altering natural dispersal rates.
Keywords
Autoregressive model, correlated environmental stochasticity, dispersal, dispersal-induced stability, metapopulation, negative binomial model, Ricker model, spatial heterogeneity, synchrony.
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Changes in forest productivity across Alaska consistent with biome shift
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Global vegetation models predict that boreal forests are particularly sensitive to a biome shift during the 21st century. This shift would manifest itself first at the biome's margins, with evergreen forest expanding into current tundra while being replaced by grasslands or temperate forest at the biome's southern edge. We evaluated changes in forest productivity since 1982 across boreal Alaska by linking satellite estimates of primary productivity and a large tree-ring data set. Trends in both records show consistent growth increases at the boreal–tundra ecotones that contrast with drought-induced productivity declines throughout interior Alaska. These patterns support the hypothesized effects of an initiating biome shift. Ultimately, tree dispersal rates, habitat availability and the rate of future climate change, and how it changes disturbance regimes, are expected to determine where the boreal biome will undergo a gradual geographic range shift, and where a more rapid decline.
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The cost of policy simplification in conservation incentive programs
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Incentive payments to private landowners provide a common strategy to conserve biodiversity and enhance the supply of goods and services from ecosystems. To deliver cost-effective improvements in biodiversity, payment schemes must trade-off inefficiencies that result from over-simplified policies with the administrative burden of implementing more complex incentive designs. We examine the effectiveness of different payment schemes using field parameterized, ecological economic models of extensive grazing farms. We focus on profit maximising farm management plans and use bird species as a policy-relevant indicator of biodiversity. Common policy simplifications result in a 49–100% loss in biodiversity benefits depending on the conservation target chosen. Failure to differentiate prices for conservation improvements in space is particularly problematic. Additional implementation costs that accompany more complicated policies are worth bearing even when these constitute a substantial proportion (70% or more) of the payments that would otherwise have been given to farmers.
Keywords
Agriculture, agri-environment scheme, biodiversity, cost-effectiveness, ecological economics, grazing, incentive
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Economic growth as the limiting factor for wildlife conservation
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The concept of limiting factor includes the lack of welfare factors and the presence of decimating factors. Originally applied to populations and species, the concept may also be applied to wildlife in the aggregate. Because the decimating factor of economic growth eliminates welfare factors for virtually all imperiled species via the principle of competitive exclusion, economic growth may be classified as the limiting factor for wildlife conservation. The wildlife profes- sion has been virtually silent about this limiting factor, suggesting that the pro- fession has been laboring in futility. The public, exhorted by neoclassical economists and political leaders, supports economic growth as a national goal. To address the limiting factor for wildlife conservation, wildlife professionals need to become versed in the history of economic growth theory, neoclassical economic growth theory, and the alternative growth paradigm provided by ecological economics. The Wildlife Society should lead the natural resources professions in developing a position on economic growth.
carrying capacity, competitive exclusion, ecological economics, economic growth, limiting factor, neoclassical economics, niche breadth, steady state economy
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Interactions and Linkages among Ecosystems during Landscape Evolution
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We synthesize our findings of studies in Glacier Bay National Park and Preserve, southeastern Alaska, to elucidate interactions and linkages among terrestrial, lake, stream, and marine intertidal ecosystems as the landscape evolves following ice recession. Development in each ecosystem is initially dominated by physical processes. Over time, biotic control becomes increasingly important, although the extent of biotic control varies among ecosystems. The changes occurring in the four ecosystems are linked by landscape processes, with the nature and strength of these linkages changing through time. Change in one ecosystem has a major influence on the nature and direction of change in other ecosystems. Soil development and woody biomass accumulation on land provide an inertia that is unmatched in stream, lake, or intertidal systems. It is important that researchers and managers understand this science of change, at different spatial and temporal scales, in order to predict future states of ecological systems. The dynamics of change that we document at Glacier Bay during primary succession have important implications for managing the system with respect to anthropogenic change.
Keywords: landscape, development, ecosystems, succession, linkages
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Effects of tree mortality caused by a bark beetle outbreak on the ant community in the San Bernardino National Forest
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Ants are used as bioindicators of the effects of disturbance on ecosystems for several reasons. First, ants are generally responsive to alteration of the biomass and diversity of the local plant community (Kalif et al., 2001) and other environmental variables (Underwood & Fisher, 2006). Second, because they occupy fixed nest locations, ants are affected by conditions on a very small scale, so that their presence and abundance are a better indicator of local conditions than are the presence or abundance of more mobile animals (Stephens & Wagner, 2006; Underwood & Fisher, 2006). Ants play important ecosystem roles and are therefore often a relevant choice for monitoring (Ho ̈lldobler & Wilson, 1990). They make up a significant percentage of the animal biomass in many ecosystems, they can be crucial to processes such as soil mixing and nutrient transport (Gentry & Stiritz, 1972), and they are important players in nutrient cycling and energy flow. Ants can also strongly influence the plant community via seed dispersal and granivory (Christian, 2001; Barrow et al., 2007). While the diversity of a given taxon is often not a reliable indicator of the diversity of other groups (Lawton et al., 1998; Bennett et al., 2009; Maleque et al., 2009; Wike et al., 2010), ant diversity is known to reflect the diversity of other invertebrates in ecosystems recovering from a disturbance in some cases (Andersen & Majer, 2004).The use of ants as bioindicators must be undertaken with caution (Underwood & Fisher, 2006). Different ant communities do not always respond to a disturbance in the same way (Arnan et al., 2009). In addition, broad measures of a bioindicator taxon, such as species richness or abundance, are potentially misleading. For instance, while it is popular to measure the species richness of bioindicator groups, the ant species richness of different habitats has been observed to respond differently to similar disturbances (Farji-Brener et al., 2002; Ratchford et al., 2005; Barrow et al., 2007), and ant species richness often does not respond at all unless disturbances are extreme (Andersen & Majer, 2004).Nonetheless, changes in the ant community can provide useful information about the responses of the ecosystem as a whole.
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Impacts of climate change on the future of biodiversity
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Many studies in recent years have investigated the effects of climate change on the future of biodiversity. In this review, we first examine the different possible effects of climate change that can operate at individual, population, species, community, ecosystem and biome scales, notably showing that species can respond to climate change challenges by shifting their climatic niche along three non-exclusive axes: time (e.g. phenology), space (e.g. range) and self (e.g. physiology). Then, we present the principal specificities and caveats of the most common approaches used to estimate future biodiversity at global and sub- continental scales and we synthesise their results. Finally, we highlight several challenges for future research both in theoretical and applied realms. Overall, our review shows that current estimates are very variable, depending on the method, taxonomic group, biodiversity loss metrics, spatial scales and time periods considered. Yet, the majority of models indicate alarming consequences for biodiversity, with the worst- case scenarios leading to extinction rates that would qualify as the sixth mass extinction in the history of the earth.
Keywords
Biodiversity, climate change, species extinctions.
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Energetic and biomechanical constraints on animal migration distance
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Animal migration is one of the great wonders of nature, but the factors that determine how far migrants travel remain poorly understood. We present a new quantitative model of animal migration and use it to describe the maximum migration distance of walking, swimming and flying migrants. The model combines biomechanics and metabolic scaling to show how maximum migration distance is constrained by body size for each mode of travel. The model also indicates that the number of body lengths travelled by walking and swimming migrants should be approximately invariant of body size. Data from over 200 species of migratory birds, mammals, fish, and invertebrates support the central conclusion of the model – that body size drives variation in maximum migration distance among species through its effects on metabolism and the cost of locomotion. The model provides a new tool to enhance general understanding of the ecology and evolution of migration.
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Biodiversity effects on ecosystem functioning change along environmental stress gradients
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Positive relationship between biodiversity and ecosystem functioning has been observed in many studies, but how this relationship is affected by environmental stress is largely unknown. To explore this influence, we measured the biomass of microalgae grown in microcosms along two stress gradients, heat and salinity, and compared our results with 13 published case studies that measured biodiversity–ecosystem functioning relationships under varying environmental conditions. We found that positive effects of biodiversity on ecosystem functioning decreased with increasing stress intensity in absolute terms. However, in relative terms, increasing stress had a stronger negative effect on low-diversity communities. This shows that more diverse biotic communities are functionally less susceptible to environmental stress, emphasises the need to maintain high levels of biodiversity as an insurance against impacts of changing environmental conditions and sets the stage for exploring the mechanisms underlying biodiversity effects in stressed ecosystems.
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Maximizing return on conservation investment in the conterminous USA
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Efficient conservation planning requires knowledge about conservation targets, threats to those targets, costs of conservation and the marginal return to additional conservation efforts. Systematic conservation planning typically only takes a small piece of this complex puzzle into account. Here, we use a return-on- investment (ROI) approach to prioritise lands for conservation at the county level in the conterminous USA. Our approach accounts for species richness, county area, the proportion of species’ ranges already protected, the threat of land conversion and land costs. Areas selected by a complementarity-based greedy heuristic using our full ROI approach provided greater averted species losses per dollar spent compared with areas selected by heuristics accounting for richness alone or richness and cost, and avoided acquiring lands not threatened with conversion. In contrast to traditional prioritisation approaches, our results high- light conservation bargains, opportunities to avert the threat of development and places where conservation efforts are currently lacking.
Keywords
Benefit cost ratio, conservation planning, economic cost, habitat protection, heuristic, land prices, reserve selection, resource allocation.
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