Habitat fragmentation generates small, isolated populations from larger ones. Plants with small or sparse populations receive fewer pollinator visits and thus produce fewer seeds. For example, smaller “island” populations of butterfly-pollinated carnation species that received fewer pollivator visits were found to produce fewer seeds than larger “mainland” populations. Because the number of genetically different mates is lower, small plant populations have higher self-fertilization (inbreeding) rates. Self-fertilization can lead to a genetic condition known as inbreeding depression. The term depression refers to the fact that in highly inbred populations, vitality decreases because more deleterious genes occur than in populations that are able to outbreed. Inbreeding depression effects can be observed after only a few generations, especially in species that normally outcross. Habitat preservation is key to keeping natural pollination systems intact and will help reduce the effects of inbreeding depression.
A second genetic condition that affects small populations, increasing their vulnerability to extinctions, increasing their vulnerability to extinction, is genetic drift. This is situation where, due to chance events, particular alleles present in a small population are lost. Genetic drift becomes a problem when the number of individuals in a population becomes lower than 250,000. Populations that are smaller than 250,000 individuals have been called “the living dead” because they have such low genetic variation that they are probably doomed to eventual extinction.
Protection of endangered species thus requires maintenance of population numbers at sufficient levels. Legal protection for plants and pollinators is provided by the Endangered Species Act in the United States, and internationally by the Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).
–an collected assay–