The preceding literature review identifies the lack of a substantial evidence base for the impacts of environmental change on diversity at the level of ecological communities, specifically: (i) focused on the meso-scale with specific reference to beta-diversity and metacommunities, (ii) focused on multi-decadal temporal scales, and (iii) comparisons of multiple biomes in the same geographical area. Therefore, within this thesis I focus on these knowledge gaps using a multidisciplinary approach. The exploration of the metacommunity concept focuses on metacommunity structure only because mutually exclusive hypotheses could not be formulated for the paradigms.
1.4.2. Aim and Objectives
My thesis aims to assess the impacts of environmental change on the diversity of ecological communities over multi-decadal temporal scales, using the spatial meso-scale. I will assess these changes in a terrestrial and a marine habitat, allowing cross-biome comparison. Furthermore, I will attempt to elucidate the relative importance of individualistic species response and community constraints. Specifically, my objectives are to:
a. Has this been addressed in conservation legislation? b. Is there evidence for its recent occurrence?
2. Assess the extent of change in inter-community (or assemblage) diversity in southern England over multiple decades as a result of environmental change.
a. Has inter-community diversity of woodland plant communities in southern England changed over 70 years? b. Has inter-assemblage diversity of temperature-sensitive
intertidal rocky shore invertebrates in southern England changed over 50 years?
For 2a & 2b:
i. Is this reflected by intra-community diversity?
ii. What are the environmental drivers of the observed change?
3. Identify the metacommunity structure of woodland plants at two points in time, seventy years apart and determine how much the structure had changed.
a. Does metacommunity structural change reflect community level changes?
4. Determine whether the climatic tracking response can be individualistically limited by the presence of physical barriers to dispersal.
a. Will the individualistic limitations alter under scenarios of future environmental change?
1.4.3. Thesis Structure
Chapter 2 addresses the first objective through discussion of the implications of the individualistic species responses on community
composition. I discuss the likelihood of non-analogous community (NAC) formation in the first direct adaptation of the concept to modern ecology (Keith et al. 2009). Within the following two chapters (3 & 4), I explore observed change in biodiversity within and between communities (objective 2) with data obtained from surveys of the same sites at two points in time. Such data provides inevitable limitations, for example, comparability of the two surveys, ‘snap-shot’ data with no time series with which to assess variability on shorter timescales, and missing or sparse data (Peterken 1992). Whilst these limitations are important considerations within my thesis they do not preclude the ability to achieve my objectives and provide valuable historical information. Specific limitations of each dataset are addressed within the relevant chapters. In Chapter 5 I address objective three through an exploration of whether the observed community changes (Chapter 3) have translated to changes in the metacommunity. Chapter 6 will focus on the process of community level biodiversity change through species level responses, specifically on the role of dispersal in establishment and maintenance of beta-diversity. The final chapter discusses the findings of each previous chapter in the context of the impact of species responses to environmental change on communities, and compares findings in marine and terrestrial habitats.
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