IB Biology Paper 3 - Ecology

Limiting Factors

parts of an ecosystem that limit the numbers of a population, these can be biotic or abiotic 

Law of Tolerance

A population’s survival depends on a set of conditions that each organism has a certain minimum, maximum, and optimum (the best) of 

Explain salt tolerance in plants

Plant growth varies depending on how much salt is in the soil (salinity levels). Cultivation of land for agriculture concentrates salt at plant roots, which makes it harder for most plants extract water from the soil and the plants intake salt which can be toxic to them. Understanding salt tolerance is therefore vital for effective crop farming.

Explain the effect of oceanic temperature rising on coral polyps

Coral polyps receive nutrients from zooxanthellae which cannot survive in very warm ocean temperatures (more than 35 ºC) which leads to coral bleaching. Most coral species therefore usually grow the best between 20-30 ºC. 

Zooxanthellae

A type of algae that gives coral polyps nutrients through photosynthesis, it lives within coral polyps’ endodermis

How to measure species distribution

• Quadrats: rectangular frames

• Transect: straight line along an abiotic setting from which data can be recorded

Ecological Niche

The range of resources and conditions allowing a species to survive

An ecological niche includes

• Habitat

• Resources

• Interactions with other species

• Activity patterns of a species

Fundamental Niche

• The entire set of conditions under which an organism can survive and reproduce (where it could live)

• This niche describes the theoretical habitat that would be perfect for the organism

Competitive Exclusionn

When 2 species share a niche, 1 species uses the resources more efficiently, causing the other species to decrease

Resource Partitioning

Both species alter their use of the niche and they divide the resources between themselves 

Realised Niche

• The set of conditions used by an organism after interacting with other species (where it actually lives)

• This niche describes the actual habitat that is occupied by an organism in the presence of competing species

Herbivory

- The act of only eating plant matter

Predation

The biological interaction where a predator hunts and consumes prey 

Symbiosis

The close and long-term interaction between 2 species

Mutualism

Both species benefit from symbiosis

Commensalism

One species benefits from symbiosis

Parasitism

One species benefits, the other is harmed from symbiosis

Keystone Species

A species that has a disproportionately large impact on the environment compared to that species’ abundance

Engineers

Species that can later their environment to aid the survival of other species

Trophic Level

The position an organism occupies within a feeding sequence

Trophic Level 1

Producer

Trophic Level 2

Primary Consumer (Herbivore)

Trophic Level 3

Secondary Consumer

Trophic Level 4

Tertiary Consumer

Food Chains

Diagrams that show the linear feeding relationships between species in a community 

Food Webs

Diagrams that show how food chains connect 

Biomass

The mass of 1 or more species

Energy Production

The rate of generation of biomass in an ecosystem

Primary Production

The production of chemical energy in organic compounds by producers 

Secondary Production

The production of biomass by consumers caused by the transfer of organic compounds between trophic levels  

Feed Conversion Ratio

• Mass of feed ÷ mass of desired output

• The lower the FCR, the more efficient the method of food conversion
  

Ecosystem

The interaction of living and non-living things within an area (all biotic and abiotic factors in an area)

Closed Ecosystem

One that can survive on its own without external influence and one that does not interact with other environments (e.g. mesocosm)

Open Ecosystem

One that exchanges both energy and matter with surrounding environments (e.g. a natural ecosystem like a forest or jungle)

Biome

An area defined by its organisms and its climate

What typically distinguish biomes

Temperature and rainfall

Tropical Rainforests

Hot and humid near the equator with high biodiversity

Taiga

Coniferous (with needles) forests near the poles that have cold temperatures and little precipitation

Deserts

Dry environments with extreme temperatures (hot and cold)

Ecological Succession

Process by which complex communities develop over time

Primary Succession

Occurs when communities develop new land without any soil to begin with (e.g. glaciers, sand dunes, etc.)

Secondary Succession

When one ecosystem is replaced by another 

Ecological Disturbance

Either natural or artificial and they cause fluctuations to the structure of ecosystems

Endemic Species

Native to a defined geographic region (e.g. Koalas in Australia)

Alien Species

• Those that have been transferred from their natural habitat to a new one (e.g. the European Rabbit in Australia)

• If these species harm their new environment, they are considered invasive

Physical Control

The physical removal or restriction of invasive species 

• Can be through fences or the removal of habitat by excavation or trimming 

• Population numbers may be reduced by hunting, trapping and culling

• Can be through fences or the removal of habitat by excavation or trimming 

Chemical Control

Control that involves the use of chemical agents (poisons and toxins) 

• May include herbicides (for plants), pesticides (for insects) or other compounds (e.g. rat poison)

• These are usually expensive 

Biological Control

Control that involves using a living organism (or a virus) to control an invasive species 

• This control may eat the species or cause it to become diseased 

Biomagnification

Process in which chemical substances become more concentrated at each trophic level 

Biodiversity

The variety of all living organisms in an ecosystem 

The Edge Effect

Edges tend to have greater biodiversity, as different habitats with different abiotic factors exist in close physical proximity. Edges tend to have more competition than central regions, which may restrict survival of certain species.

In Situ Conservation

The preservation of plant and animal species within their natural habitat

Ex Situ Conservation

The preservation of plant and animal species outside their natural habitats

Population Size is affected by:

• Natality (birth rate)

• Immigration

• Mortality

• Emigration

Indicative Species

Species that are sensitive to certain environmental conditions, giving them low tolerance. They are good for monitoring changes in the environment wen their populations increase or decrease