Authors: Achmad Ariefiandy, David M. Forsyth, Deni Purwandana, Jeri Imansyah, Claudio Ciofi, Heru Rudiharto, Aganto Seno, Tim S. Jessop
Brief summary of the paper: The roles of density-dependent and density-independent factors in the dynamics of tropical large herbivore populations are poorly understood. Understanding these dynamics is particularly important if the herbivore is prey for an apex predator of conservation concern because a decline in the prey could cause the predator to decline.
We tested hypotheses about the roles of density-dependent and density-independent factors in the dynamics of 2 tropical ungulates, Rusa deer (Rusa timorensis) and wild pigs (Sus scrofa), in Komodo National Park, eastern Indonesia. We counted the dung of Rusa deer and wild pigs (a validated index of abundance for these 2 species) along permanently marked transects at 10 sites over 4 islands annually during 2003–2014 to estimate ungulate abundance. Ungulates were much more abundant on the 2 larger islands compared with the 2 smaller islands, with wild pig dung completely absent from the latter.
During our 12-year study, Rusa deer abundance declined slightly on Nusa Kode and Rinca islands, did not change on Komodo Island, and increased on Gili Motang Island. There was a decline in abundance of wild pigs on Komodo Island and an increase on Rinca Island. Annual variation in population growth rate was strongly density-dependent and island-specific for both species, with annual rainfall and vegetation composition being relatively unimportant. Population growth rates of Rusa deer exhibited spatial synchrony, with synchrony declining with increasing intersite distance.
Our findings confirm the importance of density dependence in the dynamics of tropical large herbivore populations. However, the strength of density dependence varied between species and spatially. Declines of Rusa deer and wild pigs on the larger 2 islands, which are strongholds of the Komodo dragon, are cause for concern. Continued monitoring of ungulate populations is critical for the conservation of Komodo dragon populations in Komodo National Park.