In a recent study published in Nature, researchers assessed the global human impact on biological communities. Human activities could lead to changes in biodiversity composition across various ecosystems.
Analyzing their effects on the biological landscape of a particular region could inform conservation strategies and improve biodiversity protection efforts. Human activities, including habitat change, pollution, and climate change, cause unprecedented alterations in biodiversity.
These pressures can increase or decrease local species diversity and impact community biodiversity patterns. Human pressures lead to homogenization and differentiation, resulting in different species compositions across ecosystems.
Despite extensive research, the scale and complexity of human impacts on biodiversity remain unclear, highlighting a gap in understanding the full range of these impacts.
Additional analysis of the human activities on biodiversity and their mediation by factors such as spatial scale or type of pressure is essential for assessing mitigation actions.
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About the Study
The present meta-analysis evaluated local and global effects exerted by human activities on ecosystems and community diversity across various spaces. Researchers contrasted impacted communities with reference communities in a control-impact design.
On January 17, 2022, the researchers performed a literature search using the Science Citation Index Expanded (SCI-EXPANDED) through the Web of Science platform. This initial search resulted in 73,632 publications.
A full-text analysis for non-metric multidimensional scaling (NMDS) and principal coordinates analysis (PCoA) methods narrowed the relevant publications to 11,968.
The team evaluated distance-based unconstrained ordination plots for analysis. All included publications featured at least one plot displaying PCoA or NMDS data for the projection of biological communities calculated from a community dissimilarity matrix.
All plots reported data for reference (least impacted) and impacted groups. The team excluded restored sites, studies on seed banks, and studies involving communities reconstructed from stomach content analyses. After applying the inclusion and exclusion criteria, 32% of the selected studies were experimental, and 68% were observational.
The final dataset included 2,133 records, comprising 48,382 impacted sites and 49,401 least impacted or reference sites. This dataset enabled 3,667 comparisons of biological diversity impacts considering the five predominant human pressures, main habitats, and organismal groups.
The organisms studied included tetrapods, plants, insects, fish, fungi, and microbes inhabiting terrestrial, freshwater, and marine ecosystems. The human pressures examined were land-use change, resource exploitation, pollution, climate change, and invasive species.
Researchers determined log-response ratios, i.e., the logarithm-transformed ratios for impacted versus reference values, to obtain biodiversity metrics. They evaluated whether the impacted sites were more similar to or dissimilar from each other in relation to the reference ones (LRR homogeneity).
Subsequently, they assessed the compositional alterations in species at affected and reference locations (LRR shift). Furthermore, they evaluated local diversity changes as log-response ratios of local biodiversity (LRR local biodiversity). Mixed linear modeling enabled statistical analysis.
Results
The analysis demonstrated that human activities distinctly alter biological community composition and reduce local diversity in marine, terrestrial, and freshwater ecosystems. However, the team found no general trend of homogenization among communities.
Instead, human pressures homogenize biological communities at higher spatial levels (positive LRR homogeneity) while causing differentiation at lower ones (negative LRR homogeneity).
The direction and extent of biological diversity alterations vary significantly across different organisms, pressures, and spatial scales. Smaller species, which typically exhibit greater diversity, shorter life cycles, and higher dispersal rates than larger species, demonstrate more significant rates of community composition change.
Microbes and fungi, predominantly comprising smaller species, show the most prominent shifts in their community composition. Changes in composition become increasingly pronounced as the spatial scale decreases. Spatially closer communities are more similar on average, making them more susceptible to differentiation processes than those at higher scales.
The study also highlighted the roles of ecological drift and stochastic effects in promoting biotic differentiation, especially in local studies where intense pressures can destabilize communities.
Similar to the results for compositional shifts, pollution and habitat change are the strongest drivers of local diversity loss. However, in contrast to community composition shifts, the largest organisms experience the most adverse effects from human pressures on local-level diversity.
Lastly, the results indicate a relationship between changes in local diversity and shifts in the composition and homogenization of biological communities across space. An increase in local diversity leads to greater homogeneity and fewer shifts.
In other words, a higher species loss results in a more significantly altered composition with more differentiated communities.
Conclusions
Based on the findings, human pressures significantly alter community composition and reduce local diversity across space, leading to habitat shifts that favor certain species while disadvantaging others via environmental filtering.
The direction and magnitude of biodiversity changes vary considerably across different human pressures, organism types, and spatial scales. Smaller species, which generally exhibit higher diversity and shorter life cycles, are more susceptible to shifts in community composition.
Therefore, conservation strategies should prioritize the protection of smaller, more vulnerable species. A holistic approach considering all human pressures is essential for effectively addressing biodiversity loss and "bending the curve" on declining trends.
Understanding these pressures and their effects can help conservationists focus on local scales, promoting sustainable practices that safeguard biodiversity across various ecosystems.
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