Does movement behaviour predict population densities? A test with 25 butterfly species

Abstract

Diffusion, which approximates a correlated random walk, has been used by ecologists to describe movement, and forms the basis for many theoretical models. However, it is often criticized as too simple a model to describe animal movement in real populations. We test a key prediction of diffusion models, namely, that animals should be more abundant in land cover classes through which they move more slowly. This relationship between density and diffusion has rarely been tested across multiple species within a given landscape. We estimated diffusion rates and corresponding densities of 25 Israeli butterfly species from flight path data and visual surveys. The data were collected across 19 sites in heterogeneous landscapes with four land cover classes: semi-natural habitat, olive groves, wheat fields and field margins. As expected from theory, species tended to have higher densities in land cover classes through which they moved more slowly and lower densities in land cover classes through which they moved more quickly. Two components of movement (move length and turning angle) were not associated with density, nor was expected net squared displacement. Move time, however, was associated with density, and animals spent more time per move step in areas with higher density. The broad association we document between movement behaviour and density suggests that diffusion is a good first approximation of movement in butterflies. Moreover, our analyses demonstrate that dispersal is not a species-invariant trait, but rather one that depends on landscape context. Thus, land cover classes with high diffusion rates are likely to have low densities and be effective conduits for movement.

Cityscape quality and resource manipulation affect natural enemy biodiversity in and fidelity to urban agroecosystems

“…Our results show that cityscape effects on natural enemy communities and dispersal differ from the rural context. Drawing from diffusion theory, which predicts lower population densities in land cover that facilitates movement (Schultz et al 2017), it seems that in our system impervious cover and associated features of the urban environment favor site infidelity of individuals to the garden system. Many (possibly most) organisms move faster in the landscape matrix than in habitat patches (Kareiva and Odell 1987;Schultz 1998;Brown et al 2017;Lutscher and Musgrave 2017), attributed in part to edge effects.…”

Pre‐dispersal context and presence of opposite sex modulate density dependence and sex bias of dispersal

“…In most studies, the current density (i.e. the density observed at the beginning of the dispersal phase) is taken into account while quantifying DDD (Bitume et al 2013, Schultz et al 2017, thus neglecting the history of the population. However, dispersal can be affected by the physiology of the dispersers (Zera and Denno 1997), which in turn is expected to be a function of the pre-dispersal context.…”

Faster movement in nonhabitat matrix promotes range shifts in heterogeneous landscapes

“…All else being equal, slower movement causes animals to spend more time in a particular land‐cover type (Turchin , Schultz et al. ), which suggests a general fitness advantage of slower movement in higher‐quality habitat.…”

“…More generally, arearestricted search, in which animals move more slowly in areas where they encounter more resources, is a common movement syndrome in foraging predators (Kareiva and Odell 1987). All else being equal, slower movement causes animals to spend more time in a particular landcover type (Turchin 1991, Schultz et al 2017, which suggests a general fitness advantage of slower movement in higher-quality habitat.…”