OCR Specification focus:
‘Consider biodiversity at habitat, species and genetic levels; include examples such as sand dunes, woodland, meadows, streams, and different breeds within a species.’
Biodiversity refers to the variety of life on Earth, encompassing differences between habitats, species, and genes. Understanding these levels of biodiversity is essential for conservation and ecosystem management.
The Concept of Biodiversity
Biodiversity represents the complexity of living systems, ensuring ecosystem stability and resilience. It exists at three interconnected levels — habitat, species, and genetic — each contributing to the overall biological richness of the planet. Together, these levels describe variation from the largest ecological scales to the smallest genetic differences.
Habitat Biodiversity
Definition and Importance
Habitat biodiversity (also called ecosystem biodiversity) refers to the variety of habitats, ecosystems, and ecological niches within a particular area or across the planet.
Habitat Biodiversity: The range of different habitats or ecosystems in a given region or the world, each supporting distinct communities of organisms.
Habitats provide the physical environments in which organisms live. High habitat biodiversity supports greater opportunities for species to thrive, adapt, and interact. Variations in soil, climate, water, and geography all influence habitat diversity.
Examples
Sand dunes – characterised by shifting sandy soils and adapted plant species such as marram grass.
A sand-dune habitat on Oxwich Bay, Wales, featuring marram grass (Ammophila arenaria), a keystone dune stabiliser adapted to shifting sands. This real-world scene exemplifies habitat (ecosystem) diversity within coastal landscapes. The image is uncluttered and ideal for recognising a syllabus-named habitat. Source
Woodlands – support complex food webs, offering nesting sites, shade, and nutrient recycling.
Meadows – provide open, species-rich environments dominated by grasses and wildflowers.
Streams and rivers – contain freshwater species, from aquatic plants to invertebrates and fish.
Each habitat contributes uniquely to regional biodiversity, forming networks of ecosystems that sustain global life.
Factors Influencing Habitat Biodiversity
Climate and geography: Temperature and precipitation determine which ecosystems can develop.
Human impact: Urbanisation, agriculture, and deforestation can reduce habitat variety.
Conservation management: Protected areas and rewilding projects can increase habitat diversity.
Species Biodiversity
Defining Species Diversity
Species biodiversity represents the number and variety of species within a particular habitat or ecosystem.
Species Biodiversity: The variety of species present within an ecosystem, considering both the number of species (richness) and their relative abundance (evenness).
This level of biodiversity is most commonly used in ecological studies and provides insight into ecosystem health. Diverse communities are generally more resilient to disturbances such as disease, invasive species, or environmental change.
Components of Species Biodiversity
Species richness: The total number of different species present in a habitat.
Species evenness: The relative abundance of individuals within each species. A community with high evenness has balanced population sizes, avoiding dominance by a few species.
These components form the basis for quantitative biodiversity measures such as Simpson’s Index of Diversity (D), which assesses both richness and evenness together.
Examples
Meadow ecosystems often contain high species diversity, with grasses, flowers, insects, and small mammals coexisting.
Woodlands may have lower richness but high evenness, as competition between established tree species maintains balance.
Coral reefs are among the most species-rich ecosystems on Earth, supporting complex interdependence between organisms.
Significance
High species diversity indicates ecological stability and resistance to change.
Low species diversity can signal environmental stress or habitat degradation.
Monitoring species diversity helps ecologists evaluate conservation success and detect ecosystem threats.
Genetic Biodiversity
Definition and Role
Genetic biodiversity (or genetic diversity) is the variation of genes within and between populations of a species.
Genetic Biodiversity: The total number of different alleles present in the gene pool of a species or population, determining its potential to adapt to environmental changes.
Genetic variation arises through mutation, sexual reproduction, and gene flow between populations. It is crucial for evolutionary adaptation and long-term species survival.
Importance of Genetic Diversity
Adaptation: Populations with greater genetic diversity can better respond to selection pressures, such as disease or climate shifts.
Conservation: Low genetic diversity, often seen in endangered or isolated populations, increases susceptibility to extinction.
Agriculture and breeding: Genetic variation allows for the development of crops and livestock with desirable traits such as pest resistance or drought tolerance.
Examples
Different breeds within a species, such as domestic dogs or cattle, represent genetic variation shaped by selective breeding.
A comparative panel of four dog breeds (American Pit Bull Terrier, American Staffordshire Terrier, Staffordshire Bull Terrier, English Bull Terrier), all one species (Canis lupus familiaris). The visual emphasises genetic biodiversity expressed as contrasting morphology within a single species. Note: the collage names specific breeds, which is extra detail beyond the OCR’s generic “different breeds” phrasing. Source
Wild populations, such as cheetahs, exhibit low genetic diversity due to historical population bottlenecks, reducing adaptability.
Conservation programmes, including zoos and seed banks, maintain genetic diversity through controlled breeding and genetic storage.
Interdependence of the Levels
Although habitat, species, and genetic biodiversity are distinct, they are closely interrelated:
A diverse range of habitats allows for more ecological niches, supporting higher species diversity.
Within those species, genetic variation ensures adaptability and long-term ecosystem resilience.
Conversely, habitat destruction reduces species numbers, which in turn diminishes genetic variability.
This nested structure means conserving biodiversity requires attention at all three levels. Protecting only species without their habitats or genetic variation is insufficient for sustainability.
Measuring and Comparing Biodiversity Across Levels
Ecologists use sampling and statistical analysis to assess biodiversity:
Habitat level: Mapping ecosystems, vegetation surveys, and satellite imaging.
Species level: Field sampling, quadrats, and biodiversity indices.
Genetic level: Molecular techniques such as DNA sequencing and allele frequency analysis.
Quantifying biodiversity helps determine conservation priorities and track ecological change across time and regions.
The Value of Biodiversity at Multiple Scales
Understanding biodiversity at all levels supports practical conservation:
Local scale: Protecting specific habitats and maintaining ecological balance.
Regional scale: Managing landscape mosaics like woodlands and meadows.
Global scale: Preserving the genetic heritage of species for future generations.
In essence, biodiversity is not just about the number of species but about maintaining the intricate web of life from ecosystem to gene. High biodiversity underpins ecosystem services that sustain human life, making its study vital to both ecology and society.
FAQ
Local biodiversity refers to the variety of species and habitats within a small, defined area such as a woodland, stream, or meadow. It provides insight into the ecological health of a specific site.
Global biodiversity, on the other hand, considers the total variety of life across the planet — including all species, ecosystems, and genetic diversity.
While local biodiversity can be influenced by factors like pollution or land use, global biodiversity trends are shaped by large-scale issues such as climate change and habitat loss.
Scientists assess genetic biodiversity using molecular and statistical techniques that quantify genetic variation:
DNA sequencing identifies different alleles or mutations across populations.
Electrophoresis separates proteins or DNA fragments to compare genetic profiles.
Percentage of polymorphic loci is calculated to determine how many gene loci exist in multiple forms within a population.
These methods reveal how much variation exists within a species, which helps conservationists monitor genetic health and inbreeding risks.
Climate determines temperature, rainfall, and seasonal patterns, which directly affect the types of habitats that can exist in a region.
Geography shapes the physical landscape — mountains, valleys, coastlines, and soils — influencing both the diversity and isolation of habitats.
For example, tropical regions with high rainfall and warmth have diverse forests, while arid regions with little precipitation support sparse desert ecosystems.
In general, greater environmental variation creates more ecological niches, promoting higher habitat biodiversity.
Although many human activities reduce biodiversity, certain practices can enhance it when carefully managed:
Restoration ecology: Rewilding projects and wetland restoration create new habitats.
Traditional agriculture: Mixed cropping and hedgerow planting increase habitat variety.
Sustainable forestry: Selective logging and maintaining buffer zones preserve species diversity.
Conservation reserves: Establishing protected areas maintains natural ecosystems and connectivity between habitats.
These actions aim to mimic natural processes and restore the ecological balance that supports biodiversity at multiple levels.
High biodiversity enhances ecosystem resilience — the ability to recover from disturbance or environmental change.
Species diversity: Multiple species performing similar ecological roles mean that if one declines, others can maintain ecosystem functions.
Genetic diversity: Populations with varied genes are better able to adapt to disease or climate shifts.
Habitat diversity: Different habitats offer refuges and resources during environmental stress.
Together, these forms of diversity create a stable system capable of sustaining life even under changing conditions.
Practice Questions
Question 1 (2 marks)
Define the term biodiversity and state the three levels at which biodiversity can be considered.
Mark scheme:
1 mark: Biodiversity is the variety of living organisms in an area, including variation within and between species and ecosystems.
1 mark: Correctly identifies all three levels — habitat (or ecosystem), species, and genetic biodiversity.
Question 2 (5 marks)
Using examples, describe how biodiversity can be assessed at the habitat, species, and genetic levels. Explain why measuring biodiversity at multiple levels is important for conservation.
Mark scheme:
1 mark: Habitat biodiversity described — variety of different habitats or ecosystems in a region (e.g., woodland, meadow, stream, sand dune).
1 mark: Species biodiversity described — number and abundance of species within a habitat (species richness and evenness).
1 mark: Genetic biodiversity described — variation in alleles or genes within a population or species (e.g., different breeds of cattle or dogs).
1 mark: At least one example provided that clearly links to the correct biodiversity level.
1 mark: Explanation that measuring biodiversity at multiple levels allows comprehensive understanding of ecosystem health, adaptability, and conservation priorities.
