Abstract
The Serengeti wildebeest migration is a rare and spectacular example of a once-common biological phenomenon. A proposed road project threatens to bisect the Serengeti ecosystem and its integrity. The precautionary principle dictates that we consider the possible consequences of a road completely disrupting the migration. We used an existing spatially-explicit simulation model of wildebeest movement and population dynamics to explore how placing a barrier to migration across the proposed route (thus creating two disjoint but mobile subpopulations) might affect the long-term size of the wildebeest population. Our simulation results suggest that a barrier to migration—even without causing habitat loss—could cause the wildebeest population to decline by about a third. The driver of this decline is the effect of habitat fragmentation (even without habitat loss) on the ability of wildebeest to effectively track temporal shifts in high-quality forage resources across the landscape. Given the important role of the wildebeest migration for a number of key ecological processes, these findings have potentially important ramifications for ecosystem biodiversity, structure, and function in the Serengeti.
Highlights
The Serengeti wildebeest migration is a unique part of our biological heritage
Even without any habitat loss or increase in poaching, a partial disruption of the wildebeest migration is predicted to negatively affect wildebeest numbers, as well a cause a shift in habitat use patterns during the dry season (Fig. 3). We contrast this with the results of the no migration scenario, which predicted a collapse of the wildebeest population from an initial population of 1.2 million to less than 10% of that number over time (Fig. 4A)
One key factor underlying the superabundance of migratory ungulate populations in Serengeti is the ability of animals to efficiently track spatiotemporal variation in resource availability across landscapes with strong but noisy resource gradients [11,14,16]
Summary
The Serengeti wildebeest migration is a unique part of our biological heritage. Large-scale ungulate migrations, rare, were once commonplace across the globe [1,2,3,4]. Forage quality and food intake peak at intermediate levels of grass biomass [7,8,9,10,11], and migratory ungulates are effective at finding high-quality forage patches across heterogeneous landscapes in a range of ecosystems [5,10,11], including the Serengeti [9,12,13,14]. This ability to track transient areas of high productivity across the landscape translates into a demographic advantage for migratory animals over sedentary ones [11,15]. By disrupting movement patterns and lowering the efficiency of resource use over the annual cycle, can lead to reduced population growth and a lower carrying capacity for migratory ungulates in landscapes with high functional heterogeneity [5,13,15,16,17]
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