Geographical patterns of abundance: testing expectations of the ‘abundance optimum’ model in two taxa of ectoparasitic arthropods

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Abstract:

Abstract Aim 

The ‘abundance optimum’ hypothesis predicts that species abundance peaks in the locality with the most favourable conditions and decreases with an increase of distance from that locality. We tested this prediction for 9 fleas and 13 gamasid mite species. Location 

We used published data on fleas and gamasid mites that are parasitic on small mammals throughout the Palaearctic. Methods 

For each ectoparasite, we computed the correlation between the relative abundance on its principal host species in a region and the distance from that region to the region of maximum abundance. Then, the correlation coefficients were used in a meta-analysis. We also made a cross-species comparison between relative abundances in localities (a) closest to and (b) furthest from the locality of maximum abundance. Results 

Although the relationship between the relative abundance in a region and the distance from that region to the region of maximum abundance was negative in 19 out of 22 ectoparasites, it was only statistically significant in three of them. However, a meta-analysis of coefficients of correlations across all species revealed a significant negative effect of the distance from the region of maximum abundance on relative abundance in a particular region. A cross-species comparison between relative abundances in the localities closest to and furthest from the locality of maximum abundance demonstrated that the former were significantly higher than the latter. Main conclusions 

A lack of strict host specificity in the ectoparasites studied, and the absence of any strong spatial correlations among the environmental variables affecting ectoparasite reproduction and abundance, may provide an explanation for the spatial independence in abundance values of most species. However, a preference for a particular host even in host-opportunistic parasites combined with species-specific environmental preferences could be the reason behind the weak, but significant, negative abundance–distance relationship across species. The contradiction between results obtained when separate species were considered and when the overall pattern was analysed across species suggests that there exists a general underlying spatial pattern that can often be masked by other factors.

Keywords: Abundance; Palaearctic; ecological optimum; fleas; macroecology; mammals; mites; spatial variation

Document Type: Research Article

DOI: http://dx.doi.org/10.1111/j.1365-2699.2008.01978.x

Affiliations: 1: Mitrani Department of Desert Ecology, Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev 2: Desert Animal Adaptations and Husbandry, Wyler Department of Dryland Agriculture, Jacob Blaustein Institutes for Desert Research, Ben-Gurion University of the Negev, Midreshet Ben-Gurion, Israel 3: Department of Ecology and Environment Conservation, Omsk State Pedagogical University, Omsk 4: Laboratory of Arthropod-Borne Viral Infections, Omsk Research Institute of Natural Foci Infections, Omsk, Russia 5: Department of Zoology, University of Otago, Dunedin, New Zealand

Publication date: December 1, 2008

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