Lecture 19 Flashcards
(22 cards)
Competition
- Interaction between individuals for limited resources that reduces survival, growth, and/or fertility
- Is an inevitable consequence of increasing population size and limited resources
Intraspecific competition (with example)
- Competition between individuals of the SAME species
- E.g. Damselfish guarding territory in coral reef
Interspecific competition (with example)
- Competition between individuals of DIFFERENT species
- E.g. Two plant species competing for pollinators
Is type of competition is more common
Intraspecific competition
Why is intraspecific competition more common than interspecific
- Population = always some competition
- Reproduction requires interaction (competition for mates)
- Occupy the same region/area due to physiological requirements for habitats
What is interspecific competition long recognised to be important in
- Natural selection
- Fixation of adaptive (divergent) traits within species (competition drives to adaptive traits)
- Phenotypic divergence between species
- Abundance and distribution of species
Why may interspecific competition be reduced or eliminated over time
- Trait(s) in one (or both) species evolve (character displacement), effectively reducing the two species from competing for limiting common resources
- Note this is harder with intraspecific competition where competitors have to cohabit and reproduce together.
Interference / direct competition
- Direct interaction / contact between individuals
- Individual A has a negative effect on individual B and vice versa
E.g. Aggressive behaviour, Defending territory, Fighting for food
Exploitative / indirect competition
- Indirect interaction between individuals
- Individuals harm each other by taking up resources before others are able to
- The more resources an individuals has the higher its fitness, but the lower the fitness of other individuals competing for the limited resource pool
- E.G. Mangrove roots competing for nutrients
6 mechanisms of interspecific competition
- Consumption
- Pre-emption
- Over-growth
- Chemical interactions
- Territoriality
- Encounter Competition
Consumption
One species inhibits another by consuming a shared resource
Pre-emption
A primarily sessile (immobile) organism occupies a physical resource, therefore making it less available to others
Over-growth
- When one organism grows directly over another, with or without direct contact
- E.g. plants and competition for light
Chemical interactions (allelopathy)
chemical growth inhibitors or toxins produced to inhibit growth
Territoriality
- Aggressive behaviour to exclude others from units of space
- E.g. red wood ants in multi-party territory battles
Encounter competition
Non territorial encounters between foraging individuals
Plants vs animals
- Basic biological differences between plants (most) animals affect the process of competition
- Wide size variation in plants
- Competition for common resources
Basic biological differences between plants and animals
- Plants are sedentary so competition is generally over a smaller scale
- Immediate neighbours more impotant than size of total population
- Cant move ecological niche (restricted to resources available - animals can move :P)
Wide size variation in plants
- Size and growth of plants varies dramatically, even intraspecifically
- Variation largely depends on levels of nutrition, sun, water
- Thus, number and size of local neighbours will be very important
Competition for common resources
- All plants generally require the same essential resources (light, water, nutrients such as nitrogen, phosphorus)
- These are non-substitutable resources and therefore, competition should be more common among a wider variety of plant species
Evolving to avoid competition in plants
- Competition is important in evolution (evolve novel adaptations to avoid competition)
- Plants cant move so close neighbours tend to be related, (parent surrounded by offspring), don’t want to inhabit same space as offspring as they’ll use up resources
- Many plants evolved seed dispersal mechanisms to avoid competition
