| 1. |
- Ripa, Jörgen, et al.
(författare)
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Food web dynamics in correlated and autocorrelated environments
- 2003
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Ingår i: Theoretical Population Biology. - 1096-0325. ; 64:3, s. 369-384
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Tidskriftsartikel (refereegranskat)abstract
- The densities of populations in a community or food web vary as a consequence of both population interactions and environmental (e.g. weather) fluctuations. Populations often respond to the same kinds of environmental fluctuations, and therefore experience correlated environments. Furthermore, some environmental factors change slowly over time, thereby producing positive environmental autocorrelation. We show that the effects of environmental correlation and autocorrelation on the dynamics of the populations in a food web can be large and unintuitive, but can be understood by analyzing the eigenvectors of the community (system) matrix of interactions among populations. For example, environmental correlation and autocorrelation may either obscure or enhance the cyclic dynamics that generally characterize predator-prey interactions even when there is no direct effect of the environment on how species interact. Thus, understanding the population dynamics of species in a food web requires explicit attention to the correlation structure of environmental factors affecting all species.
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| 2. |
- Williams, C K, et al.
(författare)
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The collapse of cycles in the dynamics of North American grouse populations
- 2004
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Ingår i: Ecology Letters. - : Wiley. - 1461-023X .- 1461-0248. ; 7:12, s. 1135-1142
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Tidskriftsartikel (refereegranskat)abstract
- Cyclic dynamics of bird and mammal populations are commonly reported in northern latitudes throughout the world, and recent European observations on rodents and grouse suggest that cycle periods decline towards southern latitudes. To investigate latitudinal patterns of cyclic dynamics in North America, we assembled 27 long-term data sets collected between 1939 and 2001 for three grouse species. By fitting the data with autoregressive models to measure direct and delayed density dependence, we show that, in contrast to European studies, North American grouse exhibit period increases from north to south, with cycles collapsing via period lengthening. This occurs because delayed density dependence decreases in southern latitudes, whereas direct density dependence increases. These results show that cyclic dynamics can dissipate by period lengthening as well as the period shortening postulated for European grouse and rodents.
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