| 1. |
- Lindström, Tom, 1977-, et al.
(författare)
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Splitting the tail of the displacement kernel shows the unimportance of kurtosis
- 2008
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Ingår i: Ecology. - : Wiley. - 0012-9658 .- 1939-9170. ; 89:7, s. 1784-1790
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Tidskriftsartikel (refereegranskat)abstract
- Animals disperse in space through different movement behaviors, resulting in different displacement distances. This is often described with a displacement kernel where the long-distance dispersers are within the tail of the kernel. A displacement with a large proportion of long-distance dispersers may have impact on different aspects of spatial ecology such as invasion speed, population persistence, and distribution. It is, however, unclear whether the kurtosis of the kernel plays a major role since a fatter tail also influences the variance of the kernel. We modeled displacement in landscapes with different amounts and configurations of habitats and handled kurtosis and variance separately to study how these affected population distribution and transition time. We conclude that kurtosis is not important for any of these aspects of spatial ecology. The variance of the kernel, on the other hand, was of great importance to both population distribution and transition time. We argue that separating variance and kurtosis can cast new light on the way in which long-distance dispersers are important in ecological processes. Consequences for empirical studies are discussed.
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| 2. |
- Westerberg, Lars, 1970-, et al.
(författare)
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The effect on dispersal from complex correlations in small-scale movement
- 2008
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Ingår i: Ecological Modelling. - : Elsevier BV. - 0304-3800 .- 1872-7026. ; 213:2, s. 263-272
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Tidskriftsartikel (refereegranskat)abstract
- Calculations of large-scale displacement distances were made to evaluate the combined effect of small-scale movement pattern of a Collembola, Protaphorura armata. The effect of presence of food and conspecific density on turning angle, step length and activity/motility was investigated. Calculations of net square displacement were made both by assuming correlated random walk (CRW) and by resampling data to account for correlation structures in movement patterns that violate the assumptions of CRW. In presence of food, individuals spent less time moving (decreased activity), but when they moved they showed larger turning angles than individuals moving in areas without food. Increased conspecific density did not affect time spent moving by individuals, but when step length decreased and turning angle increased. P. armata showed negative density-dependent dispersal and exhibited area-restricted search as a response to both food and increased conspecific density. The CRW was relatively robust to some violations of its underlying assumptions. However, the expected displacement increased substantially, as much as 50%, when accounting for observed auto-correlation in step length and correlation between step length and turning angle. Hence, an explanation for increased displacement and dispersal of a species can also be the result of a more complex correlation of its behaviour rather than solely altering specific movement parameters, for example increasing step length or decreasing turning angle. The results emphasise the importance of careful analysis of small-scale movement before using them as predictors of population distribution and invasion speed in heterogeneous landscapes.
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