VMBO Year 2 · HAVO/VWO Years 2–3 · Ecology and sustainability · Section 6.3
Living together
Ecological balance
Population sizes change over time because of biotic and abiotic factors. Favourable conditions may allow growth, while unfavourable conditions may cause numbers to fall.
In a simplified model, populations fluctuate around an equilibrium level, called a biological balance. Real ecosystems can also undergo longer-lasting changes rather than returning to one fixed number.
- Population size: The number of members of a species in a particular area.
- Biotic factors: Living influences, such as food organisms, predators and pathogens.
- Abiotic factors: Non-living influences, such as temperature, soil and water.
Relationships
Individuals interact with members of their own species and other species. These interactions can bring benefits, costs or both.
- Competition: Organisms depend on the same limited resource, such as food, space or mates.
- Cooperation: Individuals work together, for example while hunting or caring for young.
Within a population
Some group-living animals have a dominance hierarchy. Established relationships can reduce repeated fighting, although group structures vary.
A territory is an area defended against others, often members of the same species, to secure food, breeding space or protection for young.
Pair formation occurs when two individuals form a reproductive partnership. Some species maintain pairs for long periods, sometimes for life.
Between species
Species may reduce competition by using different resources or being active at different times. A long-term close association between different species is called symbiosis.
Three patterns are studied here:
- Mutualism: Both partners benefit, as in the association between fungi and photosynthetic partners in lichens.
- Commensalism: One partner benefits while the other is not significantly helped or harmed, as when some algae use tree bark as a surface.
- Parasitism: The parasite benefits while the host is harmed, as when ticks feed on an animal.
Glossary
- Biological balance
- A simplified description of population sizes fluctuating around an equilibrium under relatively stable conditions.
- Commensalism
- An association benefiting one partner without a significant effect on the other.
- Competition
- Interaction between organisms relying on the same limited resources.
- Host
- An organism on or in which another organism, such as a parasite, lives.
- Mutualism
- An association in which both partners benefit.
- Pair formation
- Formation of a reproductive partnership between two individuals.
- Parasite
- An organism benefiting by living on or in a host and causing it harm.
- Parasitism
- An association benefiting a parasite at the host's expense.
- Population size
- The number of individuals of one species in a specified area.
- Dominance hierarchy
- A ranking of social relationships within an animal group.
- Cooperation
- Individuals working together, for example in hunting or reproduction.
- Symbiosis
- A close, long-term association between organisms of different species.
- Territory
- An area defended by an individual or group, often against members of the same species.