Extending ecological trap theory to account for mobile animals in dynamic environments
- Ecological traps arise when animals prefer low quality habitats. Ecological trap theory assumes animals cannot escape and that traps are permanent. But variation is ubiquitous in many ecosystems, and current theory does not account for mobile animals or environmental fluctuations.
- Nomadic animals exploit variable environments by moving between the richest patches in a landscape. They exemplify the need to improve ecological trap theory because the effects of traps on mobile populations are unknown. Under increasing anthopogenic mediated environmental change, nomads offer urgently needed insights into how animals survive in unstable environments.
- We develop a conceptual model that expands ecological trap theory to account for mobile animals in variable environments. We consider a hypothetical landscape with discrete source and sink habitats. Relative attractiveness of sources/sinks to nomads depends on a variable settlement cue (eg. pulsed food availability). In this scenario, habitat selection by nomads is represented as a continuum of preference, with sources at one extreme and sinks at the other. The model predicts that a population in this landscape could face three distinct scenarios depending on relative attractiveness of source versus sink habitats: (1) source/sink dynamics, (2) equal preference and (3) severe ecological traps.
- We test our conceptual model against six years of field data on nomadic swift parrots Lathamus discolor. A heterogeneously distributed swift parrot predator has created discrete source and sink habitats (i.e. predator absent/present respectively). We modeled parrot occupancy against annual variations in availability of their settlement cue (food) over their whole breeding range. Parrots settled wherever food was most abundant each year. By following food, swift parrots settled in both sources and sinks. Consequently, they experienced all scenarios predicted by our model within three years of the study. Because sinks predominate in the study area, swift parrots were repeatedly caught in severe or equal preference ecological traps in five of six years.
- Our conceptual model extends the theoretical framework for testing hypotheses about ecological traps for animals in variable environments. We show that population limitation in nomads is more complex than previously thought. We provide a novel starting point for further research into the conservation and evolutionary implications of chronically understudied nomads in unpredictable environments.
Online Publication Date
Journal of Wildlife Management