There is strength in diversity!

Among individual variation exemplified by alternative colour morphs of the pygmy grasshopper Tetrix subulata (photograph by Anders Forsman).

by Anders Forsman and Lena Wennersten

A better understanding of the causes and consequences of the dynamics of natural populations will allow for more efficient protection and restoration of biodiversity. It has been suggested that higher levels of phenotypic and genetic variation among individuals should promote the ecological and evolutionary success of populations and species in the face of environmental change, but this proposition has not previously been systematically evaluated.

In this study we review experimental and phylogeny-based comparative studies of plants animals and bacteria to determine whether the predictions from theory are supported overall by results from empirical investigations. The results provided strong, almost invariable, evidence that more variable populations are less vulnerable to environmental changes, show decreased fluctuations in population size, have superior establishment success, larger distribution ranges, and are less extinction prone, compared with less variable populations or species.

Some of the experimental studies included in our review comprised two or more environmental treatments. The results of these experiments indicated that the benefits of diversity are generally expressed more strongly under stressful than under benign conditions.

We also found that the relationship linking benefits to diversity is more often linear than curvilinear. Importantly, there were also exceptions. Some studies pointed to the existence of an optimal level of diversity, and others suggested that the benefits of diversity follow the law of diminishing returns.

The findings in this review may be useful for decision makers and conservationists when planning, modifying and implementing protection and management of biodiversity.

Our review also illustrated that there is a shortage of studies that can be used to evaluate the population-level consequences of diversity, as well as strong taxonomic biases with regard to study organisms. Based on our findings we identify several knowledge gaps and outline some important issues in need of further investigation.

There is ample opportunity for progress and interesting discoveries in this important and rapidly growing area of research.

Hypothesized and confirmed (numbers indicate supporting results/number of tests) direct and indirect influences of greater genetic diversity, higher levels of heritable phenotypic variation, or a larger capacity for developmental plasticity on population-level processes.

Comments