Abundance-occupancy relationships in North Sea copepods: ventures into time and space.

Abundance-occupancy relationships (AORs), namely the generally positive relationship between species’ mean local abundance and regional distribution represent the most ubiquitous macroecological pattern found in nature. Their importance lies in that they link local population processes to larger scale population structure. However, they exhibit much variability in shape and form and attempts to untangle the variety of processes proposed to underlie them indicates that interpretation of AORs is highly context specific and dependent on the temporal and spatial scales of both data and analyses.

The overarching theme of this thesis was to examine the cross-scale temporal behaviour of AORs, by using long-term copepod time-series and varying the extents and resolutions of analyses through space and time. To increase the spatial resolution of the data, I used a species distribution modeling approach to interpolation, incorporating satellite data, including measures of hydrographic structure, an important driver of plankton spatial distributions. The resulting high-resolution maps of copepod abundance distribution are an important output with wide ranging application.

I found significant heterogeneities in the relationship on decadal, inter-annual and seasonal scales, with higher-level dynamics often masking highly contrasting dynamics at lower levels. Patterns of temporal heterogeneity varied interspecifically and, consistent with theory, appear to be linked to life-history characteristics related to colonization ability. Identifying time periods or scales most relevant to species’ population dynamics allowed a better understanding of how life-history traits interact with various scales of environmental variability to generate interspecific differences in AORs.

Identification of heterogeneities is thus an important step in linking macroecological pattern to process and leads to an appreciation of the hierarchical nature of the relationship. I also demonstrated that AORs provide an excellent framework for examining the response of species’ regional population dynamics to environmental change.