Biology (External Revision)

Biodiversity,

Refers to how many different species work together in an ecosystem.

Biotic factors

living organisms

abiotic factors

physical environment

species richness

the number of species present in an ecosystem

relative species abundance

the number of individuals present for each species in an ecosystem

percentage cover

the percentage of the quadrat that a species takes up

percentage frequency

the percentage of quadrats in which a species appears

Simpson’s diversity index

the combined ratio of individuals in each species to the total individuals in an ecosystem – a quantitative measure of biodiversity

temporal scale

the time period over which an ecosystem is studied

spatial scale

how much area a studied ecosystem covers

Limiting factor

Environmental conditions (abiotic, could also be a biotic condition) that restrict how well an organism can survive and thrive in a location

clade

A group comprising all of the descendants of a particular ancestor organism

symbiosis

The relationship in which at least one species benefits from the interaction.

parasitism

one benefits, the other is harmed

commensalism

one benefits, the other is unaffected

mutualism

both benefit

photosynthetic efficiency

how well a producer converts light energy into the chemical energy of carbohydrates

autotroph (producer)

an organism that can produce its own organic compounds from sunlight, water and carbon dioxide

Energy Loss

10% of the energy at one trophic level is passed on to the next level with the rest (90%) being transformed by metabolism into heat energy and lost to the surroundings orbody waste

Calculating energy efficiency

ecological niche

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

Nitrogen Cycle

• N₂ (gas) in the atmosphere → NH₄⁺ (ammonium) by nitrogen-fixing bacteria.

• NH₄⁺ → NO₂⁻ (nitrite) → NO₃⁻ (nitrate) by nitrifying bacteria.

• NO₃⁻ → N₂ (gas) again by denitrifying bacteria.

Resource Partitioning

The creative use of space and time that reduces competition between species and allows many unique ecological niches to exist in the same area

Fundamental niche

The full potential range of conditions and resources a species can use.

Realized niche

The actual range a species occupies due to competition and other limits.

Competitive exclusion principle

No two species can occupy exactly the same niche in an ecosystem. And if so, they will compete with each other in the overlapping areas until one out-competes the other and the other retreats.

keystone species

A species that has a major impact on its ecosystem, keeping it balanced and diverse.

carrying capacity

the maximum population size of a species that can be supported in a given environment.

Population growth rate

Question: Calculate the growth rate of a population of 1000 individuals where, every year, 100 individuals are born, 65 individuals immigrate into the population, 37 individuals die and 25 individuals emigrate to another population.

Answer: 103

Lincoln Index

Random distribution

Organisms are scattered irregularly; one’s location doesn’t affect others. Common in plants.

Uniform distribution

Organisms are evenly spaced; one’s location affects how close others can be. Seen in animals with territories.

Clumped distribution

Organisms group together in patches; often due to social behavior or favorable conditions.

What is Primary succession and its steps:

Colonisation of plants on a barren land, resulted from a catastrophic event (i.e, tsunamis volcanic eruptions)

• Pioneer species (like lichens) break down rock with its acid, forming cracks in the rock allowing mosses to grow and start forming soil.

• Small plants (grasses, ferns) grow once soil develops → followed by shrubs and trees.

• Over a long time, a stable climax community (e.g., forest) forms.

r-selected

small size and fast growing organisms found during primary succession

K-selected

organisms larger in size and slow growing found during secondary succession

What is Secondary succession and its steps:

• Occurs in areas where soil already exists but vegetation has been removed (e.g., after fire, farming, floods, or human intervention).

• Plants regrow faster than in primary succession due to fertile soli and stable conditions → grasses → shrubs → trees → eventual climax community.

climax community

the end-point in a community succession where the community has become relatively stable, e.g. old-growth forests and rainforests

Features of Primary and Secondary succession

habitat fragmentation

the process by which areas of a habitat are lost, resulting in a large continuous habitat being broken up into smaller, more isolated habitats