Biodiversity and Populations Notes
Describe genetic, species and ecosystem diversity.
Genetic Diversity: The variety of genes and alleles within a population, increasing its ability to adapt to environmental change.
Species Diversity: The number of different species and their relative abundance within a community.
Ecosystem Diversity: The variety of habitats, ecosystems and ecological processes within a region.
Describe the biological species concept and identify its limitations.
Biological Species Concept: Defines a species as a group of organisms that can interbreed to produce fertile offspring and are reproductively isolated from other groups.
Limitations of the biological species cocnept: Does not work for asexual species, fossils, or cases where species don’t overlap geographically, and struggles with organisms that hybridise or have complex reproductive behaviours.
Identify the major taxa in the Linnaean system of biological classification and explain how it is used to classify and name species.
Major taxa in linnaean system: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species
How it is used to classify and name species: Classifies organisms based on shared characteristics, placing them into hierarchical taxa and giving each species a unique binomial name (Genus + species).
Use dichotomous keys to identify and classify organisms.
How to use dichotomus key: A dichotomous key is used by following paired, yes/no (or either/or) statements step‑by‑step, choosing the option that matches the organism’s features until you reach its identification or name.
Use the Lincoln index (𝑁 = 𝑀×𝑛 𝑚 ) to estimate the size of a population.
N: Estimate population size
M: Number of individuals marked and released in first sample
n: Number of indiviuduals caught second time
m: Marked indiviudlas in second capture
Determine the diversity of species using measures such as species richness, evenness (relative species abundance), percentage cover, percentage frequency and Simpson’s diversity index, 𝑆𝐷𝐼 = 1 − ( ∑ 𝑛(𝑛−1) 𝑁(𝑁−1) ).
How to determine diversity using species richness: Higher richness of one species means that there is a dominant species
How to determine diversity using evenness: High evenness = balacned ecosystem
How to determien diversity using percentage cover: Higher perecentage cover means that there may be a dominant species which affects species diversity
How to determine diversity using percentage frequency: Higher frequency shows that a specie may be mor present which afects diversity
How to determine diversity using SDI: SDI of 1 = infininte diversity, SDI of 0 = no diversity
Describe how sampling can be used to investigate the species diversity of a given area, considering the most appropriate
Sampling method: random, systematic, stratified
Random sampling: is best when the population is uniform and you want every individual to have an equal chance of selection
Systematic sampling: is best when the population list is evenly distributed and you need a fast, structured way to sample every kth member.
Stratified sampling: is best when the population has distinct subgroups that must be represented proportionally for accuracy.
Sampling technique: quadrats, line transect, belt-transect, capture-recapture
Quadrats: are used to sample stationary organisms in a uniform area to estimate abundance or distribution.
Line transects: are used when you need to record changes in species presence along an environmental gradient.
Belt-transect: are used when you need detailed data on abundance across a gradient, not just presence/absence.
Capture-recapture: is used to estimate the population size of mobile animals that cannot be counted directly.
Strategies to minimise bias: size and number of samples, random-number generators, counting criteria, calibrating equipment and noting associated precision
Size and number of samples: are chosen to ensure representative data and reduced sampling error, especially when populations are variable.
Random number generators: are used when you need unbiased, truly random selection of sampling locations or individuals.
Counting criteria: are set when you must standardise what “counts” as an organism or event to ensure consistency between observers.
Calibrating equiptment and noting associated precision: is essential when measurements must be accurate, comparable, and reported with correct uncertainty.
Measure/s of diversity.
Species richness: is used when you want a simple count of how many different species are present in an ecosystem.
Species evenness: is used when you need to assess how evenly individuals are distributed among the species present.
Simpson’s Diversity Index: is used when you want a single value that reflects both richness and evenness, giving more weight to common species.
Shannon–Wiener Index: is used when you want a sensitive measure of diversity that increases with both the number of species and how evenly they are represented.
Describe how the distribution and abundance of species in an ecosystem are influenced by
biotic factors — food availability, competition for resources, predation, disease
Food availabilty: increases abundance where resources are plentiful and limits it where food is scarce.
Competetion for resources: reduces abundance when species compete for the same limited resources and shapes distribution as organisms avoid competitors.
Predation: lowers prey abundance and restricts prey distribution to areas with fewer predators or better hiding opportunities.
Disease: decreases abundance by reducing survival and can alter distribution if outbreaks occur unevenly across the habitat.
abiotic factors — space, shelter, availability of water, nutrients, environmental conditions.
Space: limits abundance when overcrowding increases competition and determines distribution based on habitat size.
Shelter: increases abundance where protection from predators or harsh conditions is available, influencing where species can live.
Availability of water: controls abundance in water‑dependent species and restricts distribution to areas with adequate supply.
Nutrients: increase abundance where soils or waters are nutrient‑rich and limit distribution in nutrient‑poor environments.
Environmental Conditions: such as temperature, light, salinity, and pH determine where species can survive physiologically, shaping both distribution and abundance.
Explain that ecosystems are composed of varied habitats, including microhabitats, which may impact the distribution of species (e.g. uniform, random or clumped), and therefore the validity and reliability of different sampling methods/techniques.
Habitats, Microhabitats and Species Distribution: Ecosystems contain varied habitats and microhabitats that create small‑scale abiotic differences, leading species to show uniform, random or clumped distribution patterns.
Impact on Sampling Validity and Reliability: Different distribution patterns affect how accurate and consistent sampling methods are, because some techniques work better for evenly spaced, randomly scattered or clustered populations.
Interpret data from an experiment investigating how abiotic factors affect the distribution, abundance and/or biodiversity of species in an ecosystem.
Interperting Abiotic Factor Data in Ecosystems: Using experimental data on abiotic variables (e.g., light, temperature, pH, salinity, moisture) to identify how these factors influence species distribution, abundance and biodiversity, by determining whether each factor limits, enhances or shifts where species occur and how large or diverse their populations are.
Interpret data to classify and name ecosystems using Specht’s classification system and the Holdridge life zone classification scheme.
Specht’s Classification System: A vegetation‑based system that classifies ecosystems by analysing structural form and foliage cover, allowing data to be interpreted to identify the correct vegetation community.
Holdridge Life Zone Classification System: A climate‑based system that classifies ecosystems using biotemperature, precipitation and humidity, enabling data to be interpreted to name the appropriate life zone.
Identify and explain different modes of population growth, including - exponential growth (J-curve) - logistic growth (S-curve).
Exponential Growth: Population increases rapidly due to unlimited resources, producing a J‑shaped curve.
Logistic Growth: Population growth slows as environmental resistance increases, stabilising at carrying capacity and forming an S‑shaped curve.
Compare the reproductive strategies and growth curves of K- and r- strategists.
R-Strategists: reproduce rapidly with many offspring, show exponential (J‑shaped) growth and large population fluctuations.
K-Strategists: produce fewer offspring with greater parental investment, showing logistic (S‑shaped) growth that stabilises near carrying capacity.
Calculate population growth rate and change using birth, death, immigration and emigration data
Formula: Current N=Previous N+B-D+I-E
N: Population size
B: Number of births
D: Number of deaths
I: Number of immigrations
E: Number of emmigrations