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Latitudinal Gradients of Rocky Intertidal Community Structure Along The Northeast Pacific Coast: Patterns of Distributions, Abundance and Diversity

  • Author(s): Heady, Kristen Kusic
  • Advisor(s): Raimondi, Peter T
  • et al.
Abstract

A central goal of ecology is to understand the causes of spatial and temporal variation in the composition and structure of ecological communities. One way a species distribution may vary within its range is through changes in its vertical distribution. Variation in vertical distributions can influence local species abundance, which in turn can determine species ranges and the structure of communities. For my dissertation research, I investigated latitudinal gradients of rocky intertidal community structure along 5500km of coastline in the northeast Pacific Ocean. The spatially explicit design of this study allows the explicit answering of many ecological questions at a fine resolution for a large suite of species across their geographic range. By mapping the x, y, and z coordinates of intertidal species at cm scale accuracy, I determined the distribution patterns for abundance, vertical extent, and upper vertical limit of species across their range. I find the abundant center distribution, ramped south distribution and non-directional distribution are the most common distribution patterns. The distribution patterns are consistent for the majority of species between abundance, vertical extent and upper vertical limit. Next, I test the explicit hypothesis that vertical distribution of species varied progressively with latitude using linear regressions, which examined the relationship between community similarity and the vertical distribution of species. For many of the abundant species of intertidal invertebrates and algae that constitute those communities, sites that have a similar vertical distribution of species also have a similar community structure. Finally, I focus on central California to determine how the vertical distribution of species is explained by environmental factors. Of the nine abiotic factors investigated, reef slope, rock color, solar incidence, rock hardness and reef length explained the variability of species' upper limit. These abiotic factors influence the temperature of the reef which relates to desiccation stress. Whereas the vertical extent of species is explained by aspects of the reef's geomorphology that influences the abundance and reach of mobile consumers such as reef slope and rugosity. Across 32̊ of latitude, species' vertical distribution change in relation to abiotic forces and underlie the community structure patterns within the rocky intertidal.

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