Parasites and ecosystem energy flow

In this dissertation I argue that the best way to include parasites into ecological studies is by using the direct energetic costs of parasites at the individual, population, and community levels. Thus, the objective of this dissertation was to determine the direct and indirect energetic costs of parasitism within individuals, populations, and communities of hosts to assess their functional roles. To determine the energetic effects of parasites, field surveys, bomb calorimetry, and respirometry were used to create energy budgets for all species collected from streams of the New Jersey Pinelands, including all parasites. The most common parasite was Acanthocephalus tehlequahensis. At the individual and population level, this parasite significantly altered the energy allocation patterns in its isopod intermediate host and extracted 6.7% of the production energy from the isopod population (infected and uninfected hosts). However, in the definitive host, the parasite had little effect on energy allocation, and there were no significant differences in the energy budgets between infected and uninfected pirate perch hosts infected with A. tehlequahensis and the trematode Phyllodsitomum sp., and parasites within the fish population received 1.3% of the host's production energy. At the ecosystem level, energy budgets were created within two pineland streams, one with a high-level of parasitism and one with a low level of parasitism. Parasites extracted a small amount of energy from both streams (<1%), but proportionally less energy went to parasitism in the stream with low levels of parasitism. Parasite establishment may be constrained by energy flow through the food web because little energy makes it up the food web to trophic positions that parasites inhabit. This study also demonstrated that parasite species may derive their energy from many trophic levels within a food web even if they co-occur in the same host. The results of this dissertation suggest that parasites extract a small amount of energy from their hosts at all levels of ecological organization. The effects of parasites are larger because they alter energy allocation patterns of their hosts. An overall conclusion is that energetic constraints limit parasite establishment and maintenance at the ecosystem level.