Parasites: Small Players with Crucial Roles in the Ecological Theater

Abstract

Effective management of our natural resources requires an understanding of ecosystem structure and function; effectively, an ecosystem-based approach to management. Parasites occur, albeit cryptically, in almost all ecosystems, yet they are usually neglected in studies on populations and communties of organisms. Parasites can have pronounced or subtle effects on hosts affecting host behavior, growth, fecundity, and mortality. Furthermore, parasites may regulate host population dynamics and influence community structure. Many parasites have complex life cycles and depend for transmission on the presence of a variety of invertebrate and vertebrate intermediate hosts. Often transmission involves predator-prey interactions. Thus, parasites reflect the host's position in the food web and are indicative of changes in ecosystem structure and function. Parasites can provide information on population structure, evolutionary hypotheses, environmental stressors, trophic interactions, biodiversity, and climatic conditions. I use examples from diverse freshwater and marine systems to demonstrate that parasites should be incorporated into research and monitoring programs to maximize information gathered in ecosystem-based studies and resource management.

Pentastomid infection in Philodryas nattereri Steindachner, 1870 and Oxybelis aeneus (Wagler, 1824) (Squamata: Colubridae) in a caatinga of northeastern Brazil

“…Hence, phyllogenetic and ecological factors should be intimately related to patterns of infection determined by the pentastomids in the snakes studied here and by Almeida et al (2006Almeida et al ( , 2007. Environmental or anthropic interferences probably must have a significant influence on the rates of pentastomid infection in snakes, leading us to agree with Marcogliese (2004) with respect to the need for associating all ecological studies on parasites and hosts. This would contribute towards better identification and better knowledge that would be useful for management and conservation plans, mainly in neotropical regions, where such kinds of information are still scarce.…”

Seasonal occurrence of some larval stages of endoparasites in three cyprinids from the Nwanedi-Luphephe dams, the Limpopo River System, South Africa

“…Digeneans, cestodes and nematodes usually display a low specifi city to both intermediate and defi nitive hosts that ensure their wide geographical distribution. Parasites could affect the health of fi sh, growth, behavior, fecundity and mortality and also regulate host population dynamics and community structure (Marcogliese, 2004).…”

“…Ecological studies on parasites provide information about interrelationships between parasites, and their hosts about biodiversity of parasites and their distribution in a particular water system (Marcogliese, 2004;Vankara et al, 2011). The epidemiological data are particularly important when fi sh parasites are considered as the potential risks for aquaculture candidate species.…”

Diversity of metazoan parasites of the African catfish Clarias gariepinus (Burchell, 1822) as indicators of pollution in a subtropical African river system

“…Thus, healthy ecosystems can be hardly considered disease free. The fact that parasites possess complex life cycles makes them extremely valuable information units about environmental conditions, because their presence/absence tells us a great deal about not only their host ecology but also food web interactions, biodiversity and environmental stress (Overstreet, 1997;Marcogliese, 2003Marcogliese, , 2004. Combining different species based on shared patterns of transmission provides a potentially more powerful indicator of prevailing environmental conditions.…”

“…The species composition of parasite communities is clearly impacted by environmental stress, and species richness tends to decrease under degraded conditions. Numerous investigators have examined the effects of environmental stress on single species of parasites in temperate aquatic systems (Khan & Thulin, 1991;Overstreet, 1993;MacKenzie et al, 1995;Williams & Mackenzie, 2003;Marcogliese, 2004;Sures, 2004), despite the fact that it is difficult to predict the direction of effects of pollution impacts on parasite communities. Most studies document changes in some aspect of the parasite fauna, and it is clear that pollution has effects on parasite populations and communities and is, however, often associated with a reduction in species richness of parasites (Marcogliese, 2004).…”