Edge Effects & Ecological Traps

1. Edge Effects & Ecological Traps • Build upon population growth models, source-sink dynamics • Contrast edge population dynamics at the edge and core • Evaluate how selection for edge and core habitat affects population persistence

2. Edge Effects & Traps • Not all habitat is created equal • E.g. Bobolinks nest in grasslands and in hayfields • When harvested early, breeding success is lowered dramatically • Densities as high or more • Ecological trap

3. Edge Effects & Traps • So what is an ecological trap? • Most organisms occur in both high and low quality habitats (recall S-S dynamics) • However, low quality habitat does not immediately confer ‘trap’ status • It needs to be a sink and preferred • E.g. 40% of habitat is hay yet contains 60% of bobolinks

4. Edge Effects & Traps • Edges are defined as borders between two different habitat types • Core habitat is defined as habitat that is buffered some distance from an edge • Birds sometimes occur in higher densities at the edge, possibly because of increased niches and higher food • However, they frequently have higher BP and mortality rates

5. Edge Effects & Traps • Habitat edges have long been hypothesized as “ecological traps” for songbirds

6. Edge Effects & Traps • In this exercise, you will model an organism that that breeds in edge and core habitats, where each habitat type has its own, unique reproductive and survival parameters • All individuals in core habitat will have one specific rate while those in edge will have another specific rate