Environmental change is a ubiquitous feature of the conditions faced by species, so they must either evolve, move to avoid threats, or perish. Species require genetic diversity to evolve to cope with environmental change through natural selection (adaptive evolution). The ability of populations to undergo adaptive evolution depends upon the strength of selection, genetic diversity, effective population size, mutation rates and number of generations. Loss of genetic diversity in small populations reduces their ability to evolve to cope with environmental change, thus increasing their extinction risk. Adaptive evolution in the short to medium term predominantly utilizes pre-existing genetic diversity, but new mutations make increasing contributions in later generations. Evolutionary potential can be estimated from the heritability of fitness in the environment of interest, or by extrapolation from genomic diversity.
Chloroplast genomic diversity in Bulbophyllum section Macrocaulia (Bl.) Aver. (Orchidaceae, Epidendroideae, Malaxideae): insights into species divergence and adaptive evolution
