Habitat Loss: the Science Behind Dwindling Species

By Marlena Norwood

forest-path-1431297-m-1Natural habitats are dwindling because of a growing human population and increasing consumer demands. The Amazon Rainforest has decreased by 20 percent in the last 40 years.

We have discussed some effects of habitat loss in prior weeks, like how deforestation affects the water balance between soil and the atmosphere and how fewer trees means less shade for tropical animals already experiencing increased heat from climate change. But what else is at stake with loss of habitat?

To explore the relationship between habitat loss and animal populations, let’s briefly review the basics of genetics.

Genes have alleles – different forms of the same gene (like different alleles for blonde versus brown hair). Every person has a paternal and a maternal allele for each gene. Some alleles are recessive and some dominant (the blonde allele is recessive while brown is dominant). With two recessive alleles, individuals express that allele – they are considered “homozygous recessive.” With one or no recessive allele, individuals instead express the dominant allele.

Disease alleles are often recessive – disease does not affect an individual if they only have one allele, but they can still pass the allele on to their offspring (these individuals are called carriers). In large populations, it’s not as common for an individual to be “homozygous” for the disease allele (meaning they receive it from both of their parents).

But when populations are small, inbreeding occurs. When relatives mate with each other, there are more homozygous recessive individuals. The fitness of the population decreases because those homozygous individuals often die off or cannot reproduce due to being affected by the disease.

What does this have to do with habitat loss?

When trees are cut down and habitats are destroyed, it geographically isolates populations, or just limits the numbers of individuals that can survive in the smaller area. The smaller the population, the more inbreeding occurs. The fitness of the population is reduced and the population dwindles.

How can this be reversed?

panthera-pardus-amurensis-456925-m-1In the case of the Amur Leopard, an endangered species we focused on a few weeks ago, the Russian government is considering introducing captive leopards into the wild population to reproduce. However, since the captive populations are not adapted to the wild environment, re-introduction could lower the fitness of the entire Amur Leopard species, causing the population to decline even more.

The Russian government is considering adapting the captive leopards to the wild before re-introducing them. With this, the leopards may be physically prepared, but not genetically prepared, as adaptations to new environments take many generations to manifest. The re-introduced leopards therefore still may lower the fitness of the population.

Another solution? Stop destroying habitats.

The least we can do is protect the current habitats of wildlife. In protecting both terrestrial and aquatic habitats, many wildlife conservation groups need your help:

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