2.1 Introduction to Biodiversity

Biodiversity refers to the variety of different species of plants, animals, and other living organisms that exist within a particular ecosystem. It includes diversity within species, as well as between species. Ecosystems with a higher level of biodiversity are better able to respond to changes in their environment—whether those changes are short or long-term, anthropomorphic or natural—because there is better organism adaptability to disturbance.

Forms of Biodiversity

Biodiversity in its three forms—genetic, species, and habitat—is key to sustaining life in changing environments. 

Genetic Diversity 🧬

Biodiversity within a species, also known as genetic diversity, is important because it increases the adaptability and resilience of the species. Genetic diversity within a population can provide the genetic variation necessary for the population to adapt to changing environmental conditions. 

For example, if a highly genetically diverse population is infected with a specific pathogen, it is likely that at least a few individuals within the population possess some sort of immunity or enhanced ability to fight the pathogen. This allows the population to survive through the challenging environmental shift of selective pathogenic pressure. In contrast, a population with low genetic diversity may be more vulnerable to extinction because individuals will respond to the pathogen similarly based on having fewer genetic variations that may include resistance. 

Genetic diversity within a population is also important for maintaining the health and viability of the population over time. Consider a population with low genetic diversity. This species may be more prone to inbreeding, which can lead to a number of negative consequences, such as reduced fertility and increased susceptibility to disease. A more genetically diverse population with more variation has an increased number of different alleles to build resistance to ecosystem challenges. 

An increase in genetic diversity always leads to an increase in protection from environmental changes.

Population bottleneck is one way that genetic diversity may be lost. A population bottleneck is a reduction in the size of a population due to some environmental or biological factor decreasing the number of individuals. This reduction can be temporary or permanent, and it can occur over a short or long period of time. 

Some examples include:

• Natural disasters, such as earthquakes, hurricanes, or volcanic eruptions
• Human activities, such as hunting, habitat destruction, or pollution
• Diseases or epidemics, which can spread rapidly through a population and kill many individuals

Species Diversity 🐅

How does biodiversity between species, also known as species diversity, help to maintain the health and functioning of ecosystems? Different species play different roles within an ecosystem. Less diverse ecosystems are more vulnerable to collapse if exposed to extreme ecosystem events like natural disasters or drought because they lack a greater number of species that may be able to adapt to changing conditions. If one species is wiped out, there may not be another to take its place in an environment with low species diversity. 

Habitat Diversity ⛰️

Habitat diversity refers to the variety of different habitats within a particular geographic area. Habitats are the natural environments in which plants and animals live, and they can vary greatly in terms of their physical characteristics, such as temperature, moisture, and the types of plants and animals they support.

Ecosystem health is impacted by habitat diversity because diverse habitats can support a greater variety of ecological processes and functions. Habitat diversity provides a range of resources and conditions to cater to the unique needs and niches of plants, animals, fungi, and other organisms. Loss of habitat leads to a loss of specialist species, followed by a loss of generalist species. It also leads to reduced numbers of species that have large territorial requirements.

There are many ways to measure habitat diversity, including the number and variety of habitats present, the size of the habitats, and the connectivity between habitats. Habitat diversity is affected by land use practices, climate change, and natural disasters.

Richness vs Evenness

An ecosystem’s biodiversity can be measured in its richness. This refers to how many different species inhabit the ecosystem. Species richness tends to decline with distance from the equator due to climate (the poles are cold).

There are a few different formulas that calculate biodiversity, with the Simpson’s Diversity Index being the most common. Measurements range from zero to one, with one being the highest richness: 

Evenness is a measure of how the population sizes of each species in the ecosystem compare. If there are relatively equal population sizes, then the ecosystem is said to have a high evenness. However, if one species has a much larger population compared to the others, evenness is low.

This image shows two different forests. The top has a high richness (more species) but low evenness (one species has many more individuals than the others). Conversely, the bottom forest has a low richness but high evenness. Ideally, an ecosystem will have both high richness and high evenness!

Ecosystem Resistance and Resilience 

The susceptibility of ecosystems to damage is related to ecosystem resistance and resilience. Ecosystem resistance measures how much a disturbance affects the functioning of an ecosystem. The more resistant an ecosystem is, the less it will be affected by environmental changes. On the other hand, ecosystem resilience measures how quickly an ecosystem is able to recover after a disturbance. Biodiversity increases ecosystem resistance and resilience!

🎥 Watch: AP Environmental Science Streams