Abstract
Biological invasions are a leading cause of global biodiversity decline. Exotic plant invasions can have diverse effects on native plants including decreased species richness, suppressed regeneration, and altered species composition, and ecosystem processes. One specific impact of plant invasions, which has hitherto gone largely unaddressed, is the disruption of native food webs. Whereas, other impacts affect individual species or communities, food web disruption can potentially impact several trophic levels of organisms, including species at food web apices. I studied the impacts of the exotic plant Lantana camara on a tropical deciduous forest food web simplified to plants, prey and predators, where prey consisted of ungulate herbivores, and the top predator was the tiger Panthera tigris. I determined whether the invasion impacts forest vegetation, thus decreasing forage for ungulates. I also quantified differences in ungulate habitat use across a gradient of invasion severity. Finally, I addressed implications of these impacts for prey-dependent carnivores such as tigers. I found that Lantana camara invasion is associated with greatly reduced tree regeneration and grass growth. It also decreases accessibility of forage to ungulates. Further, Lantana together with livestock significantly alters the composition of understory plant communities. Finally, Lantana decreases ungulate use of habitat. The local implications are that vast tracts of globally-valued conservation landscape are in danger of losing their native plant communities, as well as their wildlife. Specifically, tigers and other large carnivores which are critically dependent on ungulates face the threat of habitat loss and prey decline. Wider implications are that exotic plants potentially impact more than just plant communities. Specifically, when an invasion is capable of decreasing the abundance of plant forage, repercussions can reach from the plant level through herbivores up to the carnivores that depend on them. Thus, systems where exotic plants adversely impact native producers are potentially vulnerable to the destabilization of food webs, in addition to impacts on individual species and communities. Such systems could also, therefore, potentially face the jeopardy of losing their carnivores. It is critical for large carnivore conservation plans to address plant invasions, and mitigate their impacts on habitat and prey.