Biodiversity (4.2.1)

Biodiversity can be considered at three levels:

• Habitat biodiversity
• Species biodiversity
• Genetic biodiversity

Habitat biodiversity is the variety of different habitats in a defined area. In general, the more habitats present in an area, the higher the biodiversity.

Species biodiversity is the variety of species within a habitat or ecosystem. It is measured in two ways:

• Species richness: the number of different species present in a habitat.
• Species evenness: the relative abundance of individuals among the different species in a habitat.

Genetic biodiversity is the genetic variation within a species or population. Genetic biodiversity is important because it increases a species’ ability to adapt to environmental changes, such as new predators, diseases, and changes in abiotic factors.

Sampling is the process of selecting a representative subset of organisms or an area in a habitat to study biodiversity.

It provides an efficient way to estimate the abundance, distribution, and diversity of organisms without examining the entire habitat.

Sampling can be used to measure:

• Distribution
• Abundance
• Traits

Sampling techniques can be random or non-random.

Types of non-random sampling include:

• Opportunistic: samples are taken from accessible organisms or locations. This is quick and easy, but may not be representative as some areas or species may be overrepresented.
• Systematic: samples are taken at fixed intervals along a line or belt transect across a habitat. Useful for studying changes in biodiversity across environmental gradients.
• Stratified: a habitat or population is divided into different strata and samples are taken from each stratum, often in proportion to its size, ensuring that all parts of the habitat are represented.

Quadrat sampling is suitable for studying plants and non-motile or slow-moving animals.

Two common techniques used when sampling with a quadrat are:

• Point frame: a frame containing evenly spaced pins is placed over the quadrat, and species touching each pin are recorded.
• Gridded quadrat: the quadrat is divided into a grid of equal sized squares. Each square is examined for the presence of specific species.

Species richness is the number of different species present within a particular area or habitat. The greater the number of species, the higher the species richness, e.g., tropical rainforest.

However, it is important to note that species richness alone can be a misleading indicator of diversity. It shows how many species are present, but does not take into account how many individuals of each species are present.

Species evenness is the relative abundance of individuals within the different species within a given area or habitat.

An area where all species have similar numbers of individuals has high species evenness, whereas an area dominated by one or two species has low species evenness.

Simpson’s Index of Diversity (D) is used to measure the biodiversity of an area by considering both species richness and species evenness.

This index provides a more accurate measure of biodiversity than species richness alone because it also takes into account the relative abundance of each species.

The equation for the Simpson’s D is:

Where:

• = total number of individuals of a species
• = total number of inidividuals of all species

Simpson’s Index of Diversity (D) ranges from 0 to 1.

Values close to 1 indicate high biodiversity, meaning:

• A large number of different species (high species richness).
• Species are fairly evenly distributed (high species evenness).
• The ecosystem is generally more stable and resilient to disturbances such as disease or environmental changes.

Values close to 0 indicate low biodiversity, meaning:

• A smaller number of species (low species richness).
• Or, one or a few species dominating the area (low species evenness).
• The ecosystem is generally less stable and more vulnerable to disturbances as the loss of can have a dramatic impact on the entire ecosystem.

Genetic diversity can be measured within a population. This is particularly important for small populations, such as those in zoos, pedigree animals, and rare breeds, where genetic diversity may be low.

Genetic diversity exists when there is more than one allele at a particular gene locus, resulting in variation between individuals within a population.

Gene loci with more than two alleles in the population are called polymorphic loci. The greater the number of alleles present at a locus, the greater the genetic diversity within the population.

Genetic diversity can be estimated by calculating the percentage of polymorphic loci in the population:

The exponential growth of the global human population has significantly impacted biodiversity by increasing the demand for natural resources such as land, water, wood, and fossil fuels.

This has led to environmental degradation, negatively affecting terrestrial and aquatic ecosystems and contributing to climate change.

The major factors reducing biodiversity include:

• habitat destruction
• habitat fragmentation
• polluting the atmosphere
• overexploitation of resources.

Modern farming practices significantly affect biodiversity.

Examples include:

• Monoculture: the cultivation of a single crop species across a large area supports fewer species compared to diverse natural habitats. A diverse area may be cleared and planted with a single species for farming.
• Selective breeding: farmers chose crops and livestock with desirable traits to breed over multiple generations. This aims to improve yield, resistance to disease, and growth rate but reduces genetic diversity over time.

Human-induced climate change is altering global climate patterns and increasing the frequency and intensity of extreme weather events such as heatwaves, hurricanes, droughts, and floods.

Many species are unable to adapt or migrate quickly enough to cope with these rapid environmental changes, leading to population declines, extinctions, and a reduction in biodiversity.

There are many economic reasons to maintain biodiversity as ecosystems perform valuable services:

• Medicines have been sourced from plants, fungi, and bacteria.
• Fresh water is purified and stored.
• The sustainable growth of timber, fuel and food.
• Maintenance of fertile soils through nutrient cycling and decomposition; monoculture depletes the same soil minerals repeatedly.

Ecological reasons to maintain biodiversity include:

• Biodiversity increases ecosystem stability, making ecosystems more resilient to environmental changes or threats.
• Keystone species have a disproportionately large effect on the structure and functioning of an ecosystem. Their loss can cause major ecosystem disruption and species decline.
• High genetic diversity enables populations to adapt through natural selection and provides a wide range of alleles for selective breeding and genetic engineering.

Aesthetic reasons to maintain biodiversity include:

• Nature’s beauty provides humans with a sense of joy and inspiration, particularly for people working in creative arts (e.g., music, poetry).
• Landscapes should be protected so they can be enjoyed by future generations.

In situ conservation focuses on protecting species in their natural environments often conserving the entire ecological community:

• National parks and wildlife reserves: protected areas are established by governments to conserve wildlife and natural landscapes. Activities such as agriculture, industrial development, and hunting are either restricted or banned (e.g., Dartmoor National Park, UK).
• Marine conservation zones: areas of ocean or coastal waters that are protected to conserve marine ecosystems. They aim to prevent overfishing, pollution, and habitat destruction (e.g., the Great Barrier Reef Marine Park, Australia).

Ex situ conservation involves protecting species by relocating them from their natural habitats to controlled environments.

Examples include:

• Zoos – can carry out captive breeding programs and research on species’ behaviour, genetics, and needs.
• Botanic gardens – plant species are grown from seeds or cuttings. Methods such as tissue culture and cloning help propagate large numbers of plants from small samples.
• Seed banks – seeds are dried and stored in temperature–controlled environments to preserve genetic diversity.

Captive populations may suffer from reduced genetic diversity and maintaining controlled environments can be costly and resource-intensive.

International agreements are essential in the global effort to conserve species and habitats. They promote cooperation, provide regulations, and incentivise conservation at different levels to ensure the protection of endangered species and their habitats.

Two examples include:

• The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES).
• The Convention on Biological Diversity (CBD).

The Convention on International Trade in Endangered Species of Wild Fauna and Flora (CITES) is an agreement signed by over 150 countries. Its primary goal is to regulate and control the trade of endangered species and their products, such as ivory.

CITES regulations aim to prevent the illegal trade of endangered species. However, concerns remain that banning trade increases the economic value of species, potentially encouraging illegal activity.

The Convention on Biological Diversity (CBD) was established during the 1992 Earth Summit in Rio de Janeiro. The convention focuses on the sustainable management of biological resources and promotes international cooperation to conserve biodiversity.

Countries that signed the CBD agreed to develop national biodiversity conservation strategies and engage in international meetings and collaborations.

Local conservation agreements exist to protect species and habitats.

The Countryside Stewardship Scheme (CSS) was initiated in the 1980s to provide financial incentives for farmers and landowners in England who adopted environmentally friendly practices:

• Protecting valuable wildlife habitats (e.g., hedgerows and buffer zones).
• Maintaining the traditional character of the land.
• Conserving natural resources and historic features.
• Supporting the conservation of traditional crops and livestock.
• Providing educational opportunities for visitors to learn about the importance of countryside biodiversity.