Geometry of the ideal free distribution: individual behavioural variation and annual reproductive success in aggregations of a social ungulate

Ecol Lett. 2020 Sep;23(9):1360-1369. doi: 10.1111/ele.13563. Epub 2020 Jun 30.

Abstract

Variation in social environment can mitigate risks and rewards associated with occupying a particular patch. We aim to integrate Ideal Free Distribution (IFD) and Geometry of the Selfish Herd (GSH) to address an apparent conflict in their predictions of equal mean fitness between patches (IFD) and declining fitness benefits within a patch (GSH). We tested these hypotheses in a socio-spatial context using individual caribou that were aggregated or disaggregated during calving and varied in their annual reproductive success (ARS). We then tested individual consistency of these spatial tactics. We reveal that two socio-spatial tactics accorded similar mean ARS (IFD); however, ARS for aggregated individuals declined near the periphery (GSH). Individuals near the aggregation periphery exhibited flexibility, whereas others were consistent. The integration of classical theories through a contemporary lens of consistent individual differences provides evidence for an integrated GSH and IFD strategy that may represent an evolutionary stable state.

Keywords: Aggregation; calf survival; caribou; geometry of the selfish herd; ideal free distribution; nearest neighbour; repeatability; reproductive success; social environment.

Publication types

  • Letter

MeSH terms

  • Animals
  • Ecosystem*
  • Population Dynamics
  • Predatory Behavior
  • Reindeer*
  • Reproduction