Data from: Does movement behaviour predict population densities? a test with 25 butterfly species

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.

近似关联随机游走的扩散（diffusion）模型已被生态学家用于描述生物运动，并成为诸多理论模型的核心基础。然而，该模型常因过于简化而饱受诟病，难以真实刻画自然种群中动物的运动模式。
我们针对扩散模型的一项关键预测展开检验，即动物在运动速度更慢的土地覆盖类型中种群丰度更高。密度与扩散之间的这种关联，在同一景观背景下的多物种种群中鲜有得到验证。
我们基于飞行轨迹数据与目视调查结果，估算了以色列境内25种蝴蝶的扩散速率及其对应种群密度。数据采集自覆盖4种土地覆盖类型的异质景观中的19个样地，分别为半自然生境、橄榄园、麦田与田埂。
正如理论预期，物种在运动速度更慢的土地覆盖类型中往往拥有更高的种群密度，而在运动速度更快的土地覆盖类型中密度则更低。运动的两个关键组分——移动距离与转向角——与种群密度并无关联，预期净平方位移亦是如此。但移动时长与种群密度存在显著关联：动物在种群密度更高的区域中，每移动步长所花费的时间更多。
我们所记录的运动行为与种群密度之间的广泛关联，表明扩散模型可作为蝴蝶运动的良好初步近似。此外，我们的分析证实，扩散并非物种固有的恒定性状，而是依赖于景观背景的可变属性。因此，扩散速率较高的土地覆盖类型往往种群密度更低，且可作为高效的物种运动廊道。