Abstract
Habitat fragmentation threatens the maintenance of genetic diversity of affected populations. Assessment of the risks associated with habitat fragmentation is a big challenge as the change in population genetic diversity is a dynamic process, often acting over long time periods and depending on various characteristics pertaining to both species (life history traits) and their populations (extrinsic characteristics). With this survey, we provide an introductory overview for persons who have to make or are interested in making predictions about the fate of forest-dwelling plant populations which have recently become fragmented and isolated from their main occurrences. We provide a concise introduction to the field of population genetics focusing on terms, processes and phenomena relevant to the maintenance of genetic diversity and vitality of plant populations. In particular the antagonistic effects of gene flow and random genetic drift are covered. A special chapter is devoted to Central European tree species (including the Carpathians) which we treat in detail with reference to an extensive literature survey on population genetic studies assembled from the whole of Europe. We further provide an overview of the population biology of associated understorey species. We conclude with recommended steps to be taken for the evaluation of potential perils of habitat fragmentation or population thinning for the genetics of tree populations. The complexity of effects exerted by life history traits and extrinsic characteristics of populations suggest population genetic development is strongly situation dependent. Therefore, we recommend following a case-by-case approach ideally supported by computer simulations to predict future population genetic development of both trees and associated understorey species.
Highlights
The area covered by European forests has fluctuated significantly over historic and recent times.Deforestation peaked in most European countries during the 18th and 19th centuries [1] and, since the forest area has increased overall [2]
The loss of population genetic diversity with genetic diversity measured as heterozygosity expected under Hardy-Weinberg-equilibrium, in contrast, is less pronounced and quantified as 1/2N per generation for genes encoded in the cell nucleus of diploids (Figure 1, [20])
In defining maintenance of pre-disturbance patternsofofpopulation population genetic genetic structure of pre-disturbance patterns structureand andlevels levels of of population genetic diversity as the conservation aim, can resort to standard population genetic diversity as the conservation aim, we canwe resort to standard theorytheory whichwhich provides provides us withrelationship an interesting relationship between gene flow genetic and population genetic The us with an interesting between gene flow and population differentiation
Summary
The area covered by European forests has fluctuated significantly over historic and recent times. In the scope of this survey, we will: (1) first provide a general introduction to these processes and explain the mechanisms by which they are acting both separately and in combination; (2) provide an introduction to traditional and more sophisticated approaches to measure gene flow, discuss their limits and summarize results available from published studies; (3) based on an extensive literature review, we will explore the role of life history traits in shaping the population genetic structure of Central European tree species and the relative sensitivity of species to habitat fragmentation; (4) further address the ultimate consequences of habitat fragmentation, i.e., the loss of genetic diversity and/or critical reduction of population size leading to inbreeding; (5) we conclude on situations considered critical for long-term maintenance of genetic diversity of fragmented populations and recommend strategies which can be followed to predict future development of their genetics.
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