Many plants rely on fruit-eating animals to disperse their seeds. This interaction benefits both the plant and the animal and is therefore termed a mutualism. Because seed dispersal can determine the abundance and range of the plant, seed dispersal mutualisms can benefit other species that use the plant for food or shelter and thus affect patterns of biodiversity across the landscape. The introduction by humans of new species into a habitat can disrupt seed dispersal mutualisms, but we know little about such disruptions may affect other, interrelated species. This project will test the larger ecological effects of disruption of an important seed dispersal mutualism in the northern temperate forests of Patagonia in Argentina. The mistletoe Tristerix corymbosus is the sole winter nectar source for the hummingbird Sephanoides sephaniodes, which remains in the region year-round and is in turn responsible for the pollination of nearly 20% of the endemic woody flora in the region. The seeds of the mistletoe are dispersed exclusively by the marsupial Dromiciops gliroides. After passing through the gut of the marsupial, most of the defecated seeds stick to branches of maqui, Aristotelia chilensis, the most abundant understory shrub in the forest and the most common host for the mistletoe. Because of these close ecological relationships, exotic species that reduce the density of maqui could also reduce the abundances of the mistletoe, the hummingbird, and the marsupial, changing the forest as a whole. This project will test the effects of the exotic wasp Vespula germanica and of exotic ungulates on maqui populations and on the linked species in the forest. Conservation of biological diversity is important to human society, and one of the major threats to biodiversity are the accidental and intentional introductions of new species around the world by humans. This research will further our understanding of how introduced species can affect biodiversity and help guide management to conserve diversity. The research will also strengthen international scientific collaboration and training.

Project Report

What happens when new species are added to ecosystems and others are lost? This is the question that Mariano Rodriguez-Cabal addressed for his dissertation research. With support by the National Science Foundation, Dr. Rodriguez-Cabal carried out a series of experiments and observations in Patagonia, Argentina to understand what happens to the interactions among really different species when exotic vertebrates and insects are introduced. The short answer is that the ecological webs that link species together begin to unravel. More specifically, Dr. Rodriguez-Cabal found that introduced deer and cattle dramatically affected a common understory plant species, which led to the reduction of one species (a host of a keystone mistletoe species), which in turn affected two key seed-dispersers (a marsupial and a bird), and a pollinator (hummingbird). In sites where the exotic cattle and deer were, we never found the endemic marsupial species; the abundance of the most common understory plant species was 16x lower; no new mistletoes were present, and finally, the abundance of a fruit-eating bird and a hummingbird were also lower in areas where the exotic deer and cattle were present. But there was another exotic species who played a part in this complicated tale as well - a wasp species that had been introduced in the 1980’s. The wasp eats the fruits of the common understory plant species. And when the wasp is present, fruit-eating birds are almost absent. As a result, the seeds of the understory plant don’t get dispersed. This interaction web - the collection of species occurring at the same place that are tied together by their interactions - begins to fall apart when species are added. Dr. Rodriguez-Cabal’s dissertation research shows how that happens and begins to illuminate the long-term consequences of the spread of exotic species. Aside from demonstrating that exotic species can unravel native ecosystems, this grant also facilitated the training of Dr. Rodriguez-Cabal and Dr. Noelia Barrios. Both are native Argentineans who received their PhDs from the University of Tennessee. Both will ultimately return to Patagonia to continue to investigate the causes and consequences of species introductions on local biodiversity. This grant has also facilitated interactions between Drs. Rodriguez-Cabal and Barrios and local stakeholders in Patagonia, ranging from policy makers, conservation practicioners, and park rangers.

National Science Foundation (NSF)
Division of Environmental Biology (DEB)
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Peter Alpert
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University of Tennessee Knoxville
United States
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