Abstract
Introduced species dominate the terrestrial isopod fauna in most inland habitats of North America, including urban landscapes. These non-native species are often very abundant and thus potentially play a significant role in detritus processing. We monitored isopod assemblages in an urban forest for a year to examine the relationship between surface activity and abiotic environmental factors, and to analyze reproductive characteristics that might contribute to their successful establishment. Using pitfall trap samples we recorded five species, two of which, Trachelipus rathkii and Cylisticus convexus, were highly abundant. We determined size, sex and reproductive state of each individual. Surface activity of both species reflected variability in abiotic stress factors for isopods, such as soil moisture and soil temperature. Early spring the main trigger was soil temperature while later in the season increasing temperature and decreasing soil moisture jointly affected population dynamics. Activity significantly correlated with soil moisture. The temporal pattern of sex ratios supported the secondary sex ratio hypothesis. Males dominated the samples on the onset of the mating season in search of females. The pattern was reversed as females searched for suitable microsites for their offspring. Size independent fecundity decreased as conditions became more stressful late in the season.
Highlights
In recent years there has been an increased interest in non-native, expansive soil invertebrates in North America
Terrestrial isopods are macro-decomposers that can significantly contribute to detritus processing and nutrient release
In this paper we report data on isopod demography in an urban forest in Baltimore, Maryland, USA
Summary
In recent years there has been an increased interest in non-native, expansive soil invertebrates in North America. Earthworms, as ecosystem engineers have multiple, profound and visible effects on soil physical and biogeochemical processes. The soil decomposer food web is complex, and other members of the fauna contribute to these processes. Soil invertebrate community structure with special emphasis of non-native species other than earthworms, has received less attention, partially because their effects on ecosystem processes may be more subtle (Niemelä et al 1997). Terrestrial isopods are macro-decomposers that can significantly contribute to detritus processing (comminution, inoculation) and nutrient release. They occur in habitats too extreme for earthworms, such as salt marshes, arid grasslands and deserts. And in other habitats they can reach extremely high local densities (e.g. Paris and Pitelka 1962, Steinberger 1976, Sorensen and Burkett 1977, Shachak et al 1979, Dias et al 2005, Messina et al 2012) elevating them to the rank of the primary detritivore grazers and keystone group in regulating fungal communities (Crowther et al 2013)
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