Competition Notes

Why Do Species Compete With Each Other?

1. Resources in ecosystems are limited.
   1. Food, space, light, water, and mates exist in finite amounts.
   2. As more individuals depend on the same resource, availability per organism decreases.
2. Competition only occurs when a resource becomes limiting.
   1. When resources are abundant, competition is weak or absent.
   2. Scarcity forces organisms to compete for access.
3. Competition directly affects survival and reproduction.
   1. Some individuals secure enough resources to survive and reproduce.
   2. Others grow more slowly, reproduce less, or fail to survive.

What Is Intraspecific Competition?

1. Individuals of the same species compete intensely because they have identical needs.
   1. They occupy the same ecological niche.
   2. They require the same food, space, and mates.
2. Intraspecific competition increases as population size increases.
   1. More individuals place greater demand on the same resources.
   2. Competition intensifies even if environmental conditions stay constant.
3. Outcomes of intraspecific competition:
   1. Reduced growth due to limited food or space.
   2. Reduced reproductive success due to limited mates or energy.
   3. Natural regulation of population size as weaker individuals fail to reproduce.

What Is Interspecific Competition?

1. Different species may have overlapping resource requirements.
   1. They may feed on similar food sources.
   2. They may occupy similar spaces within a habitat.
2. Interspecific competition shapes where species can live.
   1. One species may reduce the population size of another.
   2. Some species are restricted to smaller areas than their potential range.
3. Possible outcomes of interspecific competition:
   1. One species outcompetes another, leading to local extinction.
   2. Both species survive but at lower population sizes.
   3. Species alter resource use to reduce direct competition.

Why Do Similar Species Compete More Intensely?

1. Competition strength depends on niche overlap.
   1. Species with very similar requirements compete most strongly.
   2. Species with different niches experience little competition.
2. Competitive dominance depends on efficiency.
   1. Individuals that obtain resources faster or more effectively gain an advantage.
   2. Traits such as rapid growth, aggressive behaviour, or efficient digestion improve success.
3. Complete niche overlap cannot persist long-term.
   1. Two species cannot indefinitely depend on exactly the same limited resources.
   2. One species must change resource use or be excluded.

How Do Species Reduce Competition?

1. Resource partitioning
   1. Species share the same habitat but split the resources.
   2. Each takes a different slice: by place, type, or how they get it.
   3. For example, in one forest, birds feed at different heights.
   4. Canopy hunters take insects up high; understory birds pick from lower branches.
2. Temporal partitioning
   1. Species use resources at different times.
   2. This reduces direct interaction even when resources overlap.
   3. For example, one predator hunts during the day, while another hunts at night.
3. Evolutionary divergence
   1. Competition creates selection pressure.
   2. Traits that reduce overlap increase survival and reproduction.
   3. Over generations, species become more specialised.
   4. For example, Darwin’s finches evolved different beak shapes to exploit different food sources.

How Does Competition Influence Evolution?

1. Competition acts as a selective pressure.
   1. Individuals with advantageous traits survive more often.
   2. These traits are passed on to future generations.
2. Competition can increase biodiversity.
   1. Resource partitioning allows multiple species to coexist.
   2. Specialization reduces direct conflict.
3. Competition can also reduce biodiversity.
   1. Dominant competitors may exclude weaker species.
   2. Local extinction occurs if adaptation is not possible.

What Determines The Outcome Of Competition?

1. Adaptations
   1. Physical traits such as size or speed.
   2. Behavioral traits such as territorial behaviour.
   3. Physiological traits such as tolerance to limited resources.
2. Niche breadth
   1. Generalists use a wide range of resources.
   2. Specialists rely on a narrow range of resources.
   3. Generalists often cope better with changing conditions.
3. Environmental conditions
   1. Changes in habitat or climate can shift competitive advantage.
   2. A species dominant under one condition may lose dominance under another.

Example

Grey squirrels outcompete red squirrels because they can digest acorns more efficiently.

What Happens When Competition Is Reduced Or Removed?

1. Reduced competition can increase population sizes.
   1. More individuals gain access to resources.
   2. Growth and reproduction rates increase.
2. Removal of a dominant competitor can increase diversity.
   1. Previously suppressed species may expand.
   2. Resources become more evenly distributed.