Do species display characteristic intraspecific levels of patchiness in a given habitat type? The case of intertidal sea
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ORIGINAL PAPER
Do species display characteristic intraspecific levels of patchiness in a given habitat type? The case of intertidal seagrass macrobenthos R. S. K. Barnes1,2,3 Received: 5 August 2020 / Accepted: 16 October 2020 © The Author(s) 2020
Abstract Intertidal macrobenthic assemblages associated with monospecific stands of Zostera muelleri, Cymodocea serratula, Halodule uninervis and Halophila ovalis seagrasses are known to display uniform spatial patchiness on the Moreton Bay coast of North Stradbroke Island, Queensland, as do those in Z. capensis in the Knysna estuarine bay, South Africa. Thirty-seven historical datasets of these macrobenthic assemblages were re-analysed to assess variation of local patchiness in each of the 18 most common individual assemblage components at each of these localities in terms of three metrics: overall patchiness (Lloyd’s index of patchiness), levels of unoccupancy, and variation in abundance across occupied samples (Lloyd’s index of mean crowding). Within-site patchiness was not caused by a restriction of individual species to specific subareas but by variation in their local density, particularly by the extent of unoccupied ‘interstitial’ spaces within patches. Especially in the more uniform Queensland conditions, the more common species occurred relatively widely across the whole locality; individual samples from which a given species was absent never themselves formed patches, the number of such samples conforming to points on truncated normal curves of the frequency of occurrence. Of the 36 species investigated, the two most abundant and widespread both in Queensland and in South Africa displayed significant or near-significant uniformity of levels of local patchiness, whilst five showed significantly uniform mean crowding and ten significantly uniform unoccupancy. This is the first demonstration that some species may display a characteristic level of patchiness in a given habitat type.
Introduction Patchiness is the norm in biological systems; patchiness of the habitat, patchiness of resources, patchiness of organismal numbers (Wiens 1989; Kotliar and Wiens 1990). It also Responsible Editor: F. Bulleri. Reviewed by G.M. Martins and an undisclosed expert. Electronic supplementary material The online version of this article (https://doi.org/10.1007/s00227-020-03793-9) contains supplementary material, which is available to authorized users. * R. S. K. Barnes [email protected] 1
School of Biological Sciences and Centre for Marine Science, University of Queensland, Brisbane, QLD, Australia
2
Department of Zoology and Entomology, Rhodes University, Eastern Cape, Makhanda, Republic of South Africa
3
Department of Zoology and Conservation Research Institute, University of Cambridge, Cambridge, UK
occurs at all spatial scales such that patches are themselves patchy (Kotliar and Wiens 1990; Morrisey et al. 1992). These spatial patterns have been much studied in seagrass systems, particularly in relation to anthropogenicallyinduced habitat fragmentation (Be
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