Acknowledging the importance of variability we want to shift the focus from ‘average’ movement towards incorporating possible effects of individual variation in movement properties and decisions for biodiversity dynamics. We expect that this will not only advance our mechanistic understanding of how biodiversity patterns emerge but also improve our ability to predict biodiversity responses to ongoing changes in land use or climate. However, given the large variation of movement types (e.g. foraging, dispersal, migration, passive transport, movements to find a mate, defend a territory or nomadic movements) and their potential impact on different levels of biodiversity at different spatiotemporal scales, there is a strong need for a conceptual framework that allows for a better integration of movement ecology into biodiversity research (Jeltsch et al. 2013). A suitable starting point is provided by the conceptual framework for movement ecology related to focal individuals introduced by Nathan et al. (2008). In this framework the authors distinguish between three basic components related to the focal individual, i.e. internal state, motion capacity, and navigation capacity that are affected by various external factors (summarized as a fourth basic component). The resulting movement path of the individual feeds back to the internal and external components. Extending this framework to biodiversity research requires the addition of key links showing how moving individuals might impact biodiversity. To this end, we apply a theory-driven interface between movement ecology and biodiversity research that is based on two elements (Jeltsch et al. 2013): the ‘mobile links’ concept (Lundberg & Moberg 2003), and the concept of ‘equalizing’ and ‘stabilizing’ coexistence mechanisms (Chesson 2000).
The concept of ‘mobile links’ was originally developed to describe how moving animals provide links between communities and ecosystems that otherwise remain separate (Lundberg & Moberg 2003). Based on what animals primarily transport and translocate between areas, these links have been categorized as resource, process, and genetic links. Prominent examples for mobile resource links are seabirds concentrating nutrients via guano deposits. Process linkers provide new or intensify existing ecological processes. Examples include predation or grazing of large mammals or herbivorous birds, which affect nutrient cycling, biomass production, disturbance regimes and consequently plant species composition. Genetic linkers mainly transfer ‘genetic material’ into a community, e.g. by transporting genes within active dispersers, seeds, propagules, microbiota or other organisms. The mobile links perspective provides a functional perspective, i.e. the movement of individuals is investigated with respect to its effects on other processes that impact biodiversity.
The concept of ‘equalizing’ and ‘stabilizing’ mechanisms enables a general categorization of mechanisms of biodiversity emergence and maintenance (Chesson 2000). In particular, stabilizing and equalizing mechanisms provide a unifying ‘currency’ for translating the effects caused by moving individuals to species coexistence and biodiversity. In the context of movement ecology, equalizing mechanisms refer to effects of moving individuals that reduce large average fitness differences between individuals of competing species and thereby contribute to stable coexistence. Following the concept of Chesson (2000), equalizing mechanisms slow down species’ exclusion while, in contrast, stabilizing mechanisms actually lead to stable coexistence. The latter occurs when they include an ‘increase-when-rare’ process, i.e. when local populations have a positive effective growth rate at a low density. Examples of such stabilizing mechanisms are predators switching their focal prey species at low prey densities or other non-linear density-dependent feedback loops, where negative interactions are reduced at low densities. In agreement with classical ecological theory, stabilizing mechanisms lead to coexistence since they increase negative intraspecific interactions relative to negative interspecific interactions. Typically, a combination of equalizing and stabilizing mechanisms is active in maintaining species diversity in a given system.
Chesson, P. (2000). Mechanisms of maintenance of species diversity. Annual Review of Ecology and Systematics, 31:343–366.
Jeltsch, F., Bonte, D., Pe’er, G., Reineking, B., Leimgruber, P., Balkenhol, N., Schröder, B., Buchmann, C.M., Mueller, T., Blaum, N., Zurell, D., Böhning-Gaese, K., Wiegand, T., Eccard, J.A., Hofer, H., Reeg, J., Eggers, U., Bauer, S. (2013b). Integrating movement ecology with biodiversity research - exploring new avenues to address spatiotemporal biodiversity dynamics. Movement Ecology, 1:6.
Lundberg, J., Moberg, F. (2003). Mobile link organisms and ecosystem functioning: implications for ecosystem resilience and management. Ecosystems, 6:87–98.
Nathan, R., Getz, W.M., Revilla, E., Holyoak, M., Kadmon, R., Saltz, D., Smouse, P.E. (2008). A movement ecology paradigm for unifying organismal movement research. Proceedings of the National Academy of Sciences of the United States of America, 105:19052–19059.