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Urbanization and Protected Areas
by Liz Nichols
Spring 2005

When faced with human activities leading to ecological degradation, the most commonly invoked conservation response is to create a protected area.  The land surrounding protected areas is called a matrixand can be used in a variety of ways, such as farming, logging, or urban or suburban development.  Understanding the influence of a human-dominated matrix on the ecosystem functioning of protected areas is crucial if we are to maintain the ecosystem services human economies and welfare depend upon.  In my Master’s thesis at Columbia University, I sought to understand the impacts of matrix urbanization on a group of insects that mediates a suite of crucial ecosystem services: dung beetles.

Adults of the two families of globally distributed and ecologically crucial dung beetles (Aphodiinae and Scarabaeinae) feed on mammalian dung and lay their eggs in balls made by rolling bits of the dung away and burying them underground.  In this way, beetles conduct a series of ecosystem services, including nutrient recycling and waste removal, soil conditioning and aeration, suppression of dung-dwelling vertebrate parasites, and secondary seed dispersal.

In 2003, I sampled both dung beetles and the dung flies with which they compete for access to dung resources.  When present in abundance, dung flies prevent dung beetle females from laying eggs on the dung.  The study involved 50 sites: 10 in contiguous forest (Black Rock and Sterling Forest ) and 10 forest fragments in each of four different matrices in New York and New Jersey : fragmented forest, agricultural lands, suburban, and urban.  Using pitfall traps baited with fresh dung, I captured more than 3400 dung beetles (12 species) and 2300 dung flies (11 morphospecies, or clearly unique, though unidentified, species).

I found that as the matrix surrounding the protected areas became increasingly urbanized, the species richness of native dung beetles declined while that of non-native species increased, and the total abundance of dung beetles dropped dramatically, reaching its lowest point in suburban and urban parks.  Conversely, the number of fly species increased along the urbanization gradient, and the number of individuals reached its peak in urban areas.  Thus, urbanization appears to shift the scales in favor of dung flies, reducing the ecosystem services mediated by dung beetles.  Though short term and limited in scope, this study suggests that the creation of protected areas without regard to the surrounding matrix may fail to preserve all of the ecosystem services upon which we depend.

Liz Nichols received her Masters in Conservation Biology from Columbia University in 2004.  She is an Invertebrate Biodiversity Specialist with the Center for Biodiversity and Conservation of the American Museum of Natural History.