2 research outputs found
Interactions between all pairs of neighboring trees in 16 forests worldwide reveal details of unique ecological processes in each forest, and provide windows into their evolutionary histories
When Darwin visited the Galapagos archipelago, he observed that, in spite of the islands’ physical similarity, members of species that had dispersed to them recently were beginning to diverge from each other. He postulated that these divergences must have resulted primarily from interactions with sets of other species that had also diverged across these otherwise similar islands. By extrapolation, if Darwin is correct, such complex interactions must be driving species divergences across all ecosystems. However, many current general ecological theories that predict observed distributions of species in ecosystems do not take the details of between-species interactions into account. Here we quantify, in sixteen forest diversity plots (FDPs) worldwide, highly significant negative density-dependent (NDD) components of both conspecific and heterospecific between-tree interactions that affect the trees’ distributions, growth, recruitment, and mortality. These interactions decline smoothly in significance with increasing physical distance between trees. They also tend to decline in significance with increasing phylogenetic distance between the trees, but each FDP exhibits its own unique pattern of exceptions to this overall decline. Unique patterns of between-species interactions in ecosystems, of the general type that Darwin postulated, are likely to have contributed to the exceptions. We test the power of our null-model method by using a deliberately modified data set, and show that the method easily identifies the modifications. We examine how some of the exceptions, at the Wind River (USA) FDP, reveal new details of a known allelopathic effect of one of the Wind River gymnosperm species. Finally, we explore how similar analyses can be used to investigate details of many types of interactions in these complex ecosystems, and can provide clues to the evolution of these interactions
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Is fine-scale fire disturbance better for insect populations? Evaluating population growth rate in response to management plans for an endangered butterfly metapopulation
Prescribed fire is used in fire-adapted ecosystems to reintroduce lost disturbance processes. Controlled burns create a mosaic of habitat features in the landscape for species endemic to these systems. Observed population responses of animals following disturbance are often described, but mechanistic population models that incorporate vital rates to understand and predict how spatially different fire regimes affect population dynamics are needed to develop optimal management scenarios. We assessed how an insect metapopulation responds to fire disturbance of varying spatial scales and intensity. Specifically, we test whether fine-scale disturbance increases population growth rate relative to large-scale burning, whether the response changes with fire intensity, and whether fine-scale disturbance decreases extirpation risk. In addition, we test whether eggs laid by immigrant butterflies relative to surviving residents are important drivers of population recovery post-fire. We tested seven management scenarios for an endangered butterfly, Fender's blue (Plebejus icarioides fenderi). We developed a spatially-explicit agent-based model for a metapopulation in Oregon, USA incorporating demographic vital rates, habitat-specific movement rules, and a dynamic effect of fire disturbance to quantify population dynamics and dispersal patterns for each scenario. Our approach of a spatially-explicit agent-based model demonstrated mechanisms by which fire-sensitive insect populations respond and recover from prescribed fires. Population recovery after fire in small populations is driven by immigrant individuals, and more intense disturbance generates extremes in population dynamics. We found fine-scale disturbance is better for population growth rate and large-scale disturbance increases extinction risk. Fire regimes should be applied at fine scales in the landscape to achieve boosts in population growth for rare, fire-sensitive insects