On defining and quantifying biotic homogenization (original) (raw)
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Biotic homogenization and changes in species diversity across human-modified ecosystems
Proceedings of the Royal Society B: Biological Sciences, 2006
Changing land use and the spread of 'winning' native or exotic plants are expected to lead to biotic homogenization (BH), in which previously distinct plant communities become progressively more similar. In parallel, many ecosystems have recently seen increases in local species (a-) diversity, yet g-diversity has continued to decline at larger scales. Using national ecological surveillance data for Great Britain, we quantify relationships between change in a-diversity and between-habitat homogenizations at two levels of organization: species composition and plant functional traits. Across Britain both increases and decreases in a-diversity were observed in small random sampling plots (10-200 m 2 ) located within a national random sample of 1 km square regions. As a-diversity declined (spatially in 1978 or temporally between 1978 and 1998), plant communities became functionally more similar, but species-compositional similarity declined. Thus, different communities converged on a narrower range of winning trait syndromes, but species identities remained historically contingent, differentiating a mosaic of residual species-poor habitat patches within each 1 km square. The reverse trends in b-diversity occurred where a-diversity increased. When impacted by the same type and intensity of environmental change, directions of change in a-diversity are likely to depend upon differences in starting productivity and disturbance. This is one reason why local diversity change and BH across habitats are not likely to be consistently coupled.
Ecological and Evolutionary Consequences of Biological Invasion and Habitat Fragmentation
Ecosystems, 2005
Biotic homogenization, the gradual replacement of native biotas by locally expanding non-natives, is a global process that diminishes floral and faunal distinctions among regions. Although patterns of homogenization have been well studied, their specific ecological and evolutionary consequences remain unexplored. We argue that our current perspective on biotic homogenization should be expanded beyond a simple recognition of species diversity loss, towards a synthesis of higher order effects. Here, we explore three distinct forms of homogenization (genetic, taxonomic and functional), and discuss their immediate and future impacts on ecological and evolutionary processes. Our goal is to initiate future research that investigates the broader conservation implications of homogenization and to promote a proactive style of adaptive management that engages the human component of the anthropogenic blender that is currently mixing the biota on Earth.
Natureza & Conservacao, 2011
Definitions of Biodiversity that encompass multiple levels of the biological hierarchy are common and fulfill theoretical and conservation expectations. However, these definitions are usually not fully operational because these levels are usually analyzed independently. We understand that the difficulties in integrating concepts and methods for distinct "Fundamental Biodiversity Units" (FBUs) for analyses, including genes, haplotypes or neutral molecular variants, species, biomes or ecosystem, arise both because of operational and conceptual difficulties in dealing with the evolutionary continuum and because of 'sociological' issues regarding how different research traditions in Ecology and Evolutionary Biology deal with these different FBUs. Here we explore some common patterns of geographic variation in FBUs at different hierarchical levels, starting from the conceptual view by which evolution give rises to a continuum of biodiversity. We seek for an integrated methodological and conceptual framework to study FBUs, searching for the relationships and commonalities of concepts and methods traditionally developed to evaluate patterns and processes at a given level of the biological hierarchy. We point out several cases where conceptual and theoretical advances have been made by using an integrated perspective based for FBUs, for the analysis of broad-scale gradients in richness, distance decay similarity and systematic conservation planning. We conclude by stating that the recognition of an integrated approach that takes the evolutionary continuum into account may be an important step to mitigate biodiversity loss.
Environmental Conservation, 2019
SummaryWe combined tools of phylogeography, population genetics and biogeographical interpretation to analyse a group of phylogenetically independent lineages (animals and plants) that coexist within the same geographical region, yet under markedly different environments, in order to identify generalized barriers for gene flow. We tested the hypothesis that major geographic features have produced a concordant genetic structure in phylogenetically independent lineages. A rigorous bibliographic search was performed, selecting available molecular information from six taxa occupying distinct southern biomes of South America: Yungas, Prepuna, Puna and northern Monte. We estimated within-population genetic diversity, the genetic structure and haplotype phylogenies to assemble distribution maps of genetic barriers for each species. We found a strong association between genetic variation and latitudinal distribution of populations. We detected a major barrier for six taxa at 27°S latitude a...
Biological diversification and its causes
Cracraft, J. (1985) Biological diversification and its causes. Ann. Missouri Bot. Gard. 72: 794-822., 1985
Three major patterns of diversity are defined and a general hypothesis proposed to explain them. These patterns include (a) macroevolutionary diversity, encompassing temporal changes in species richness within and among clades, (b) global diversity, in which gradients of diversity among communities or biotas vary spatially and temporally, and (c) Phanerozoic diversity, which describes largescale temporal variation in species richness within the entire biosphere. Current explanatory hypotheses for these patterns are generally formulated for systems that are assumed to be in a state of ecological equilibrium, with speciation and extinction rates being diversity-dependent. This paper describes an alternative model of diversification in which speciation and extinction rates are independent of standing diversity.
Frontiers in Ecology and Evolution, 2018
Current approaches to biodiversity conservation are largely based on geographic areas, ecosystems, ecological communities, and species, with less attention on genetic diversity and the evolutionary continuum from populations to species. Conservation management generally rests on discrete categories, such as identified species, and, for threated taxa, intraspecific units. Species, in particular, provide a common measure of biodiversity yet in both theory and nature, speciation is typically a protracted process progressing from connected populations to unambiguous species with variable rates of phenotypic, ecological and genetic divergence. Thus, most recognized species are not genetically uniform and are sometimes highly structured into historically isolated populations worthy of consideration as intraspecific units that represent unique genetic diversity for conservation. Genome screens offer unprecedented resolution of structure across taxonomic boundaries in species complexes, and have the potential to oversplit species if not interpreted conservatively. This highlights the blurred line between populations and species, and can confound simple dichotomies of "species" vs. "not species." At the same time, like plants, there is increasing evidence that even distantly related animal species can hybridize and exchange genes. A review of conservation legislation reveals that legal definitions of "species" are quite flexible and can accommodate a range of infra-specifictaxa and divergent populations, as well as taxonomically recognized species. For example, the legislative definition of a species around the world can include: species, subspecies, varieties, and geographically and/or genetically distinct populations. In principle, this flexibility allows for protection of genetic diversity and maintenance of evolutionary processes at a broad range of infra-specific levels. However, evolutionary biologists often fail to adequately justify and then translate their evidence for genetically defined units into categories suited to assessment under local legislation. We recommend that (i) genomic data should be interpreted conservatively when formally naming species, (ii) concomitantly, there should be stronger impetus and a more uniform approach to identifying clearly justified intraspecific units, (iii) guidelines be developed for recognizing and labeling intraspecific data that align with best scientific practice, and (iv) that the more nuanced view of species and speciation emerging from genomic analyses is communicated more effectively by scientists to decision makers.
Journal of Biogeography, 2010
Aim Within a region, different habitat types are characterized by different species and some habitat types have higher species diversities than others. Different habitat types are also characterized by different phylogenetic clades. However, it is not known whether – within a given region – some habitat types have species pools that are more phylogenetically diversified than others. We investigated whether species pools in contemporary habitat types represent different levels of diversification of angiosperms and, if so, whether these differences correlate with particular environmental factors. We tested these relationships in a region of recent geological origin possessing a comparatively young flora, and compared the result with standard analyses of species diversity.Location The Netherlands.Methods We studied angiosperms across the full range of habitat types present in the Netherlands. We characterized levels of diversification represented in species pools within each of these habitat types with respect to (1) taxonomic diversification, i.e. the rate of increase of richness across taxonomic ranks (relative to a null expectation for a given species richness), and (2) cladogenic diversification, i.e. the average cladogenic distance of species from the root of a phylogenetic tree of the species pool within a given region.Results Species pools of different habitat types represented different levels of taxonomic and cladogenic diversification. These differences were strongly correlated with the environmental characteristics of the habitat type. Greater levels of taxonomic diversification were represented in the species pools of relatively dry and open habitat types. Greater levels of cladogenic diversification were represented in habitats with both dry and weakly acidic soils. The relationship between environmental factors and taxonomic and cladogenic diversification (r2 = 0.88 and 0.76, respectively) was stronger than that between environmental factors and species richness (r2 = 0.34).Main conclusions Within a region, species resulting from particularly high rates of diversification accumulated in particular habitat types. These habitat types represent specific contemporary abiotic environments and have a tighter relationship with levels of diversification than with species richness.
Diversity and Distributions, 2010
Aim In an era of global habitat loss and species extinction, conservation biology is increasingly becoming a science of triage. A key approach has been the designation of global biodiversity hotspots – areas of high species richness and endemism – prioritizing regions that are disproportionately valuable. However, traditional hotspot approaches leave absent information on species evolutionary histories. We argue that prioritizing the preservation of evolutionary diversity is one way to maximize genotypic and functional diversity, providing ecosystems with the greatest number of options for dealing with an uncertain future.Location Global.Methods We review methods for encapsulating phylogenetic diversity and distinctiveness and provide an illustration of how phylogenetic metrics can be extended to include data on geographical rarity and inform conservation prioritization at biogeographic scales.Results Abundance-weighted metrics of evolutionary diversity can be used to simultaneously prioritize populations, species, habitats and biogeographical regions.Main conclusion Policy makers need to know where scarce conservation funds should be focused to maximize gains and minimize the loss of biological diversity. By incorporating these evolutionary diversity metrics into prioritization schemes, managers can better quantify the valuation of different regions based on evolutionary information.