Can livestock grazing dampen density dependent fluctuations in wild herbivore populations?

Conservation policy for the high mountains of Asia increasingly recognises
the need to encompass large multi-use landscapes beyond the protected area
network. Due to limited long-term research in this region, our
understanding of even fundamental processes, such as factors regulating
large mammal populations is poor. Understanding the factors that regulate
animal populations, especially those generating cyclicity, is a
long-standing problem in ecology. Long-term research across multiple taxa
(mainly from Europe and North America) has focused on the relative roles
of food and predation in generating cyclicity in population dynamics. It
remains unclear how trophic interactions that are influenced by
anthropogenic stressors can affect population dynamics in human-modified
landscapes.  We present a 10-year study to compare the effects of
livestock grazing on density dependent dynamics in two populations of
bharal, Pseudois nayaur, in the Himalaya. We combine this with a
mechanistic understanding of whether density dependence in these two sites
acts predominantly by affecting adult survival or recruitment. We compared
and quantified density dependence in the bharal population by fitting
Bayesian Gompertz state‐space (GSS) models. We found evidence for negative
density dependence which indicates possible cyclic dynamics in the bharal
population of the site (Tabo) with low livestock density. The population
dynamics of this site were driven by recruited offspring – with a 2-year
density dependent lag effect – rather than adult survival. In the site
with high livestock density (Kibber), this density dependence was not
detected. We postulate the potential role of excessive grazing by
livestock in affecting offspring recruitment, thereby affecting the bharal
population in Kibber. Synthesis and applications: Our results suggest that
conservation action to facilitate wild herbivore population recovery, such
as the development of protected areas and village reserves, needs to
account for density dependent regulation. Sites with trophy hunting
require continuous monitoring to understand the effects of density
dependence so that appropriate hunting quotas can be formulated.