Life on earth is currently undergoing one of the largest mass extinctions our planet has seen. Human activities affect the natural world in a number of ways; we destroy natural habitats, move species around the globe, and are causing global warming. Because of this, many species of plants, animals and fungi are declining in numbers and face extinction.
It is vitally important to reduce our environmental impact and to try and conserve natural ecosystems, local and global biodiversity. One of our biggest tools which can help us to do so is our understanding of ecology and evolution.
The Evil Quartet
A biologist called Jared Diamond coined the phrase ‘the evil quartet’ to describe the four main human-induced causes of extinction: habitat degradation and fragmentation, introduction of exotic species and over harvesting.
Habitat degradation and fragmentation include wetland destruction, river pollution, deforestation of woodlands and rainforest, and even just the isolation of pockets of forest as roads are built through them. These changes affect species in a number of ways. They are associated with reductions in population sizes and increased isolation of populations as well as, potentially, novel selective pressures.
The introduction of exotic species can result in a rapid increase in numbers of the invasive species, at the cost of native species which are either out-competed or introduced to novel diseases. Such has been the case for native red squirrels in the UK since grey squirrels were introduced from north America. Changes can frequently have knock-on effects throughout the local environment.
Over harvesting, such as of fish stocks like North Atlantic Cod, can rapidly reduce the population size and impose very strong directional selective pressures on a species. The result can be rapid and large shifts in the size and age at which the species matures and how quickly the individuals grow. Again, these changes can lead to wider effects across the ecosystem.
Key Processes & Contemporary Evolution
Conservation science, like all biological fields, is underpinned by evolutionary theory. Overharvesting, habitat degradation and destruction share a number of features which are key components and processes in natural evolutionary biology. Species which are overharvested or which live in disturbed environments often show a reduction in population size, a reduction in genetic diversity and reduced gene flow between smaller populations. These are known to have a number of effects. A reduced population size means that mutations are more likely to be lost or fixed by chance rather than selection, which can impede adaptive responses to selection pressure. Reduced genetic diversity can do the same, and increased inbreeding can lead to the accumulation of mutations which negatively affect the health and survival of individuals in a population, putting them at further risk of extinction.
Isolation of populations can have other effects over and beyond gene flow. Whilst in some circumstances it may increase the rate of local adaptations, it can also lead to an increase in inbreeding. It can also mean populations becoming so isolated that random fluctuations in population size cannot be stabilised by immigrants so the populations is at greater risk of dying out.
Invasive species face similar problems when they first colonise a new habitat. Their population size will usually be small, probably with reduced genetic diversity and little or no gene flow with other populations. Because of this, immediately after a colonisation event population numbers of the invasive species remain small. But if they are able to persist and adapt to the local environment they may then rapidly increase in population size.
So, to combat invasive species we should tackle them early on in their colonisation event before they get past the problems of having a small population. To conserve species which face over harvesting and habitat destruction we need to help them overcome these same problems. Our understanding of evolution can help us to do this.
For example, studies of micro-arthropods in artificial moss ‘islands’, and experiments on butterflies, have shown that habitat ‘corridors’ can be used to inter-connect patches of undisturbed regions which would otherwise be isolated from each other. This has been shown to promote gene flow and increase the effective population size and immigration/emigration rates. This practice has the potential, if widely implemented, to reduce local extinction rates.
A common strategy to conserve species threatened with extinction is to create a captive or wild ‘refuge’ population to use as a kind of backup in case wild populations go extinct. These refuge populations also suffer from reduced population sizes, and may evolve away from optimal fitness for their wild habitat. To prevent this, policies which allow some gene flow between wild and refuge populations could be implemented.
It may also be possible to use these refuge populations to create a population which is better adapted to the changing conditions in the wild than are wild populations. By artificial selection or by exposing them to less extreme changes over a number of generations, when released, these individuals may be better able to survive in the wild.
Finally when boosting dwindling wild populations with individuals either from refuge or other wild populations we also need to consider what effects this will have. Perhaps the dwindling population has some local adaptation, or has purged most of its deleterious mutations! Introducing foreign individuals could break up local adaptation or spread new deleterious mutations amongst a small population so leading to inbreeding depression.
Conservation And Cambridge
Conserving natural habitats and species in the face of expanding human populations and global warming is our greatest challenge in the modern world. To be successful conservation biologists depend on our knowledge of various evolutionary processes to design and implement successful rescue plans for threatened species
Many scientists working in Cambridge are attempting to tackle conservation issues. There is a large conservation science group working in the Zoology Department and other individual research groups, such as Dr. David Coomes’ Lab also work on conservation issues. Researchers from the university have also combined with local conservation and wildlife groups to form the Cambridge Conservation Initiative which carries out research and education, and advices on policy formation for the conservation of biodiversity and ecosystems.
Written by Stephen Montgomery
References & Further Reading
The Future of Life
by Edward O. Wilson, Abacus:2002