12 Biology - Unit 3

Population

The number of a specific species that live in a specific region

Community

Consists of different species living in the same environment / ecosystem

Ecosystem

Is a system formed by living organisms (biotic factors) interacting with one another and their physical environment (abiotic factors).

Biodiversity

The number, variety, and variation of genes, species and ecosystems on earth.

Genetic Diversity 

The variety of genes within a species.

Species diversity

The vairiety of different species living in one area (usually an ecosystem).

Ecosystem diversity

This is the variety of different ecosystems in a region / area.

Biological Species Concept

A species is a group of similar organisms that can interbreed in nature to produce fertile offspring and are reproductively isolated from other groups

Biological Species Concept for Asexual Reproduction

Doesn’t work for organisms that reproduce without mating, such as bacteria

Hybridisation

Sometimes, closely related species can produce a viable offspring

Extinct Species

Hard to apply biological species concept since there is no observational data

Ring Species

Each population can breed with its neighbours, but populations at opposite ends can’t breed with each other, even though they’re linked by a chain of interbreeding populations.

Parthenogenesis

Reproduction where males are not needed. Involves Females getting self-fertilised

Things that Limit Biological species concept

• Asexual Reproduction

• Hybridsation

• Extinct Species

• Ring Species

• Parthenogenesis

Binomial nomenclature

Used to name organisms using their genus and specifc names. 

Dichotomous Key

A tool used by biologists to identify and classify organisms based on their characteristics.

Species richness

The number of different species within an area.

Species evenness / relative species abundance

The relative abundance of different species in an area.

Species Diversity (SDI or Simpsons Diversity Index)

Takes into account both the number of species present (richness) and the number of individuals per species (evenness). The closer the value to 1, the higher the diversity.

Assumptions of Lincoln Index

• Closed population

• All individuals have an equal chance of being caught

• Marks are not lost, damaged, or overlooked

• Sufficient time for mixing

• Sample size is large enough

Biotic Factors affecting population and species diversity in ecosystems

• Food availability

• Competition for Resources

• Predation

• Disease

Intraspecific

Competition within the same species for resources

Interspecific

Competition between different species for resources

Abiotic Factors affecting population and biodiversity in an ecosystem

• Space

• Shelter

• Availability of Water

• Nutrients

• Environmental Conditions like pH, temperature, light levels, etc.

Habitat

The environment of which an organism lives in

Microhabitat

Small, specialised part of a larger habitat.

Distribution of Species

Determined by the habitat patchiness (distribution of resources) and features of the organisms themselves, such as territoriality in animals or autotoxicity in plants.

Uniform Distribution

When individuals are evenly spaced throughout a habitat, often due to competition for resources. 

Random Distribution

When individuals are spaced randomly within a specific region with no consistency or specific pattern. This is usually seen in species with an abundance of resources and little interaction between individuals.

Clumped Distribution

When individuals are clustered together, often due to social behaviour, resource availability, or environmental factors.

Law of Tolerance

For each abiotic factor, an organism has a range of tolerances within which it can survive.

Holdridge Life Zone

Classifies global ecosystems (life zones) based on climate factors that determine vegetation type.

Specht Vegetation Classification

Describes vegetation structure in Australia based on plant height and foliage cover

R Strategists

• Short life

  • reproduce quickly before environmental change.

• Rapid Growth

  • allows them to take advantage of resources.

• Early maturity

  • helps reproduce before predators.

• Many Offspring

  • quantity over quality, increased chance of population growth.

• Little Parental Care

  • parents conserve energy for next reproduction cycle.

• Pioneers / colonisers

  • prepare environment for later species to live.

• Generalists

  • survive on wider range of resources and can withstand wider range of conditions

• The population is controlled by density independent factors such as climatic events of fires / droughts, etc.

  • eg: •After rain → puddles form → millions of mosquitoes hatch = population boom.

    •When it dries out → puddles evaporate → eggs and larvae die = population crash.

K Strategists

• Long life

• Slower growth

  • helps compete for food and territory

• Late maturity

  • help them learn from parents before reproduction

• Fewer Offspring

• High Parental Care

  • helps care for young in tough conditions

• Later stages of concession

  • move into environments that are already liveable (not pioneer species)

• Niche Specialists

  • don’t cope well with sudden changes

• Population is controlled by density dependant factors (competition / predation, etc). 

  • when too much individuals living in same area increase competition, disease, and predation.

Exponential Growth Pattern

An exponential growth patter (J curve) occurs in an ideal, unlimited environment.

• Under ideal conditions with unlimited resources, a population will growth exponentially.

• Exponential growth does not happen in natural populations for very long because the resources get used up.

• Population growth slows down when food and space become more difficult to find (competition).

Trophic Levels

An organisms position in a food chain.

Producers → Primary Consumers → Secondary Consumers → Tertiary Consumers → Quaternary Consumers

How is energy lost between Trophic Levels

• Respiration (released as heat)

• Movement and activity

• Waste (uneaten parts, excretion). 

Roles of Decomposers in Ecosystems and Food Chains

Decomposers break down waste to recycle nutrients from the waste for the ecosystem to reuse.

Food Chains

Show the order of trophic level and flow of energy

Food Webs

A complex network of interrelated food chains

Ecological Pyramids

Represent how energy of biomass is distributed across trophic levels.

Why isn’t all sunlight used as energy by plants

Plants can’t absorb all of it since the wavelengths which emit green light would be reflected. 

Predation

One organism (the predator) hunts and kills another organism (the prey) for food. (

Competition

Occurs when two or more organisms compete for the same limited resource (e.g. food, water, shelter, mates.).

Mutualism

A relationship where both species benefit.

Commensalism

One species benefits while the other is unaffected (neither harmed nor benefited).

Parasitism

One species (the parasite) benefits while the other (the host) is harmed.

Ecological Niche

The role and space that an organism fills in an ecosystem, including all its interactions with the biotic and abiotic factors in an environment.

Fundamental Niche

All the potential resources that a species can use in its environment.

• Requires the absence of competition.

Realised Niche

Some habitats and resources are not available because competitors occupy them.

• This is what the species actually uses. 

Competitive Exclusion Principle

The exclusion of a species from a community by another organism better adapted to that particular ecological niche.

• When one species has even the slightest advantage over another, the one with the advantage will dominate in the long term.

Niche Partitioning

Niche partitioning happens when different species share the same habitat but use it in different ways This reduces competition and allows them to live together. 

Keystone Species

A plant or animal that plays a unique and crucial role in the way an ecosystem functions

• they have an influence on an ecosystem that is disproportionate to their abundance.

Carrying Capacity

Is the population size that can be supported indefinitely on the available resources and services of that ecosystem. 

Limiting Factor

A limiting factor is an abiotic or biotic factor that restricts the number of individuals in a population

• because of these limiting factors, each ecosystem has a finite capacity for growth connected to its carrying capacity.

Ecological Succession

The change in structure and species composition of a community over time.

• All successions involve changes in structure and function until a climax community (end point of the ecological succession)1 is reached

Pioneer Species

• Ability to fixate nitrogen

• Tolerance to extreme conditions

• Rapid germination of seeds

• Ability to photosynthesise efficiently.

Climax Community

Final state of the ecosystem in the stage of ecological succession with little change in species composition and change in ecosystem.

Primary Succession

Ecological succession onto regions that have never been colonised and involves no habitats

Secondary Succession

Refers to reintroduction of organisms (pioneer species) into an ecosystem that may have been destroyed completely and made uninhabitable.

Overexploitation

Harvesting species or resources from the wild at rates faster than natural populations can recover.

Habitat Destruction

Occurs when natural habitats are no longer able to support the species present, resulting in the displacement or destruction of its biodiversity

Monocultures 

The agricultural practice of producing or growing a single crop, plant, or livestock species.

Pollution

All forms of pollution (air, water, soil, noise, chemical, etc.) pose a serious threat to biodiversity - they harm living organisms and damage ecosystems.

Holdridge Life Zone

Classifies global ecosystems (life zones) based on climate factors that determine vegetation type. 

Specht Vegetation Classification

Describes vegetation structure in Australia based on plant height and foliage cover. 

Random Sampling

This is where each member of the population is equally likely to be included

You need to use a random number table or random number generator to select numbers

Systemic Sampling

Samples are taken from uniform intervals throughout an area.

Stratified Samping

The process of identifying areas within an overall habitat, which may be very different from each other and which need to be sampled correctly.

Quadrats

Frames of known size that are used to sample vegetation or small organisms in a specific area. They are often used to estimate population density or to study distribution of plants or sessile organims.

Line Transect

A line transect involves laying a straight line through a habitat and counting the organisms that touch or are close to that line to estimate their abundance.

Belt Transect

It involves laying a straight line (transect line) through a habitat and recording all the organisms found within a set width (belt) along that line - for example, 1m wide.

4 ways to Minimise Bias

• Size and number of samples

• Random Number Generator

• Counting Criteria

  • what is counted in the sample (one leaf presented in one quadrat, is that counted?)

• Calibrating Equipment

Percentage Cover

This tells us how much space a species occupies in a particular sample we take. 

Percentage Frequency

Is the probability that a species will be found within a single quadrant.

Water Cycle

• Rain falls in rivers and soil which runs down and is absorbed which goes out into the ocean to be evaporated into the sky, which is condensed into clouds, eventually forming rain.

Carbon Cycle

Nitrogen Cycle

Gene Flow

• Gene flow is the movement of alleles between populations when individuals migrate and reproduce.

• Gene flow changes allele frequencies by moving alleles between populations.

• This can increase variation and alter the characteristics of a population over time.

Genetic Drift

• Genetic drift is a random drift in allele frequencies within a population due to chance events.

• Unlike natural selection, genetic drift is not driven by environmental pressures or adaptation.

• Genetic drift changes allele frequencies through random chance, particularly in small populations

• This can alter a population’s genetic makeup over time and cause microevolution.

Bottleneck Effec

Sudden event drastically reduces the population size.

Founder Effect

A random portion of population somehow seperates from a larger population and establishes a new population.

Mutations

Mutations are the random changse in an organism’s DNA sequence which cause genetic variation in populations as they introduce new alleles into a population, needed for microevolutionary change.

Cladograms

A cladogram is a branching diagram that shows hypothesised evolutionary relationships between organisms.

• It is based on shared derived characteristics not simply overall similarity.

Phylograms

Shows common ancestry just like a cladogram.

• Branch lengths have meaning. Longer branches indicate more evolutionary change (e.g., more DNA mutations or genetic differences).

• Often constructed using DNA, RNA, or protein sequence data.

Adaptive radiation

Evolutionary radiation

Evolutionary radiation is the rapid diversification of species from a common ancestor

• Often follows mass extinctions or environmental shifts that leave niches vacant.

Divergence

Evolutionary change that causes a species to become more and more dissimilar overtime.