Modularity along organism dispersal gradients challenges a prevailing view of abrupt transitions in animal landscape perception

Ana Inés Borthagaray, Juan Manuel Barreneche, Sebastián Abades and Matías Arim. Ecography. DOI: 10.1111/j.1600-0587.2013.00366.x.


A common property of landscapes and metacommunities is the occurrence of abrupt shifts in connectivity along gradients of individual dispersal abilities. Animals with short-range dispersal capability perceive fragmented landscapes, but organisms moving across critical thresholds perceive continuous landscapes. Th is qualitative shift in landscape perception may determine several attributes of local communities and the dynamics of whole metacommunities. Modularity describes the existence in some communities of relatively high numbers of mutual connections favoring the movement of neighboring individuals (even when each individual is able to reach any patch in the landscape). Local patch linkages and metacommunity connectivity along gradients of dispersal ability have been reported frequently. However, the intermediate level of structure captured by modularity has not been considered. We evaluated landscape connectivity and modularity along gradients of individual dispersal abilities. Random landscapes with diff erent degrees of cell aggregation and occupancy were simulated; we also analyzed ten real ecosystems. An expected, a shift in landscape connectivity was always detected; modularity consistently decreased gradually along dispersal gradients in both simulated networks and empirical landscapes. Neutral metacommunities within simulated landscapes demonstrated that modularity and connectivity may refl ect landscape traits in the shaping of metacommunity diversity. Average beta-diversity was strongly associated with modularity, particularly with low migration rates, while connectivity trends tracked changes in betadiversityat intermediate to high migrations rates. Consequently, while some species are able to perceive abrupt transitions in the landscape, many others probably experience a gradual continuum in landscape perception, contrary to predictions from previous analyses. Furthermore, the gradual behavior of modularity indicates that it may represent an exceptional early-warning tool that measures system distance to tipping points. Our study highlights the multiple perceptions that different species may have of a single landscape and shows, for the fi rst time, a theoretical and empirical relationship between landscape modularity, and metacommunity diversity.


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