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From pristine forests to logged areas: Why are beta-diversity outcomes so different in different environments?
β-diversity is an important concept in ecology, which represents the ratio of regional and local species diversity. The term was first coined by R.H. Whittaker, who introduced it along with α-diversity and γ-diversity. This suggests that total species diversity (γ) in a landscape depends on two different factors: mean species diversity at the local level (α) and variation between local sites (β). However, β-diversity may show very different results in different environments.
β-diversity can be described as a measure of species turnover, reflecting the variation in species composition between different sites or communities.
Measurements and types of β-diversity
β-diversity can be measured in several ways, the simplest definition of which can be expressed as:
β = γ / α
This means that when we know the total species diversity of the entire dataset (γ) and the average species diversity of each subunit (α), we can calculate β-diversity. However, over time, ecologists have developed more different calculation methods and definitions, which means that β-diversity no longer has a single form.
Differences in β-diversity patterns
While understanding variation in species composition from local to regional scales is a central issue in ecology and biogeography, studies often reach conflicting conclusions. For example, some theories predict that β-diversity would be higher at lower latitudes. In the Danum Valley of the Margaret Mountains, Kitching et al. collected moths from primary forests and logged forests and found that β-diversity was higher in primary forests than in logged forests. However, research by Berry et al. found that among tree samples in the same area, the β-diversity of logged forests was higher than that of original forests.
The study shows significant differences in colour and diversity between communities, complicating our understanding of biodiversity.
According to a recent quantitative review, beta diversity in primary forests is similar to that in a variety of anthropogenically altered sites, such as secondary forests, plantations, pastures, and cities. Therefore, it seems that there is still room for improvement in the consensus on β-diversity patterns. Some researchers, such as Sreekar et al., believe that these inconsistencies are mainly due to differences in spatial scale and granularity among studies, and they showed that spatial scale changes the relationship between β-diversity and latitude.
Diversity partitioning into past geological periods
In geological history, major evolutionary events in species diversity are often associated with changes in the relative contributions of α-diversity and β-diversity. For example, the Cambrian Explosion and the Paleo-Aldwich diversification events, and their subsequent post-extinction recovery. Empirical data from these cases support theoretical predictions: an increase in the number of species will increase β-diversity relative to α-diversity, primarily due to the effects of interspecific competition. However, once options for increasing geographic turnover are exhausted, α-diversity may increase again.
This further emphasizes the dynamic balance of species diversity in ecosystems and its impact on species survival and ecosystem functioning.
Among many biodiversity measures, β-diversity is particularly susceptible to human activities. Activities such as logging, urban development, and agricultural expansion will change the original ecosystem, causing species to be redistributed due to environmental changes. This has in turn sparked discussions on how to reasonably protect the diversity and function of ecosystems.
However, as β-diversity is studied in depth, ecologists are beginning to pay more attention to changes in species composition and explore how to more effectively compile biodiversity maps to maintain or improve overall ecological health. This has also given rise to new concepts, such as Zeta diversity (ζ-diversity), which are used to more comprehensively connect the various existing patterns of biodiversity.
Faced with such a complex and dynamic ecosystem, we can't help but think: How can we protect and promote species diversity in a changing environment to achieve ecological sustainability and stability?
