intraspecific competition Flashcards
Definition
outcome of individuals or groups of individuals of the same species occupying and sometimes guarding/exploiting resources. As population density increases mortality rates increase after a period of ‘density independence’ intraspecific competition increases until carrying capacity is reached.
Closely linked to resource density – when population is low there may be no interspecific competition but this will increase as population reaches capacity.
why does it occur?
Organisms of the same species occupy the same niche using up resources such as food or light, preventing others from doing so.
Population size is kept in carrying capacity (k) of an area by resource limitations (either realised or perceived)
2 main forms
2 main forms
Direct interference – physical interaction in competition for resources e.g. stag rut. Independent of resource scarcity and leads to high competition – direct competition can occur even when resources are plentiful
Indirect exploitation – use of slow replenishing resources creates resource depletion zones where resources are limited (or percieved to be limited or patchy)
Overall competition within an area is influenced by intra and interspecific competition contributing to survival and evolution of species (Darwin Origin of Species)
Different niches at different life stages decreases intraspecific competition
Example damselfly:
larvae – aquatic hunters
adults -flying predators
no overlap in resource dependence
Intraspecific competition can lead to higher or lower variation within a population.
Example: sticklebacks
In an experiment where sticklebacks were put into unnaturally high population in lake enclosures
(stanback and bolnick 2006)
- Fast moving individuals exploited the usual resources
- Others exploited previously unused resources
- This resulted in higher genetic diversity
^ Conversely it can select for lower variation in other species as only some phenotypes can exploit available resources most efficiently
Why model intraspecific competition
Helps us understand how competition affects a population
Useful for predicting how a population will change in response to stimuli
Improves understanding of the ecology of a species to support conservation/sustainable harvesting
For example: ant colonies with neighbouring colonies produce more soldier pupa than those without neighbouring competitors
Carrying capacity – a useful tool for modelling whole populations
- Carrying capacity of a habitat for a species is determined by two things:
-Amount of resources available
-Intensity of competition for those resources - Carrying capacity exceeded –> Competition leads to death of excess individuals
- Carrying capacity can change over time-why?
-Change in resources available
e.g seasonality or natural disaster
-Change in competition intensity e.g breeding season
High competition can result in reduced growth rate
Modelling effects on individuals
- Effects on individual growth often density dependent
- Models may need to be tailored to study species
- Often assume that all individuals are equal competitors
this is not the case! - Individual-based modelling used for this
- Gives very high-res, accurate output-but much data needed
^Tailored model of study species required
e.g. for maize - variation affecting ability to defend territory or grow largest leaves to take the most light available etc.
Game theory modelling
Often difficult to isolate competitive effects in real populations
Game theory-mathematical models of strategy that can be expressed in words
Can help us model behavioural strategies used in intraspecific competition
Consider competitive interactions in terms of numerical cost-benefit on individual fitness
Modelling the behavioural strategies used in intraspecific competition
Example: Maynard-Smith
Hawk and dove strategy – Hawk types physically attack opponents (high physical risk)
Dove types fight in song (low physical risk)
Both strategies lead to equal fitness in the two species
https://college.holycross.edu/faculty/kprestwi/behavior/ESS/HvD_intro.html
Behavioural strategies of individuals are therefore influenced by conspecifics
Methods of study of intraspecific competition
Long-term studies observe changes in population dynamics, resource availability, and competition over time
In the field: Quantified observations on conflicts, resources, territories and the type of competition in a natural habitat. As well as measurements of individual organism strength
In the laboratory: The availability of resources can be manipulated
Quantifying behaviours in the field
To assess conflicts whether direct or indirect 4
- approaches are highly situational
- specific to species and situations
Example 1: Bower bird creates decorative ‘bower’ displays and the quality is defined by design and objects – males will steal objects from other bowers - success of males could be determined by their thieving activities
Example 2: cheetah males mark territories, using GPS collars it was possible to determine territory boundaries and where they interact
Territory mapping
Territories are essential for an understanding of competition
Individuals may defend a territory for its potential resources against conspecifics
Assessing and quantifying resources within a territory and if they can carry the population
Mapping with GPS or radio transmitters (larger animals)
Mapping individual visible territories e.g. cichlid fish create hexagonal territories which can be measured
Understanding populations
Stable isotope analysis to determine dietary niches within species e.g. young fish are not in competition with adult fish due to different diet choices
Mark and recapture methods also used
Genetic studies
Using genetic markers to observe gene flow within population
Provide insights into mating behaviours
Provides insight into niche adaptation within a species
Example: genetic variability within one species of chickpea
Studies in laboratory
Resource manipulation
Advantages of controlled conditions in labs
Example: Intraspecific competition counters the effects of elevated and optimal temperatures on phloem-feeding insects in tropical and temperate rice
Behavioral observations
Observing aggression, dominance, and mate competition in a controlled environment.
Effects of intraspecific competition on species
Impacts behaviour, physiology and population size
Physiology study Example
Red Grouse testosterone fluctuation according to breeding season results in physical changes (causing red comb above eye to become enlarged)
Red grouse: Lagopus lagopus scotius, males participate in physical competitions over territory. Territory = access to resources and breeding opportunities. These competitions occur in spring and autumn –outside of the breeding season. Individuals without territory are unlikely to mate, therefore making success in these competitions critical.
There is a positive correlation between testosterone levels and success in territorial competition. Testosterone levels in male red grouse fluctuate seasonally, peaking in October and April at the height of the competition season.(Canoine, V. et al., 2005.)Increased testosterone leads to physical and behavioural changes e.g. enlarged red comb adornments and increased aggression.
Behaviour study example
Chimpanzee hierarchy, lower ranking males will be more submissive and dominant more aggressive even to those that rank higher than them. Alphas will mediate arguments and organise the troupe. Chimpanzees (Pan trogolodytes) live in groups of 10-150 members. Complex social hierarchies, led by a dominant “alpha” male. Female chimpanzees also have a hierarchy with an “alpha” female. Dominance in males is usually established through displays e.g. charging, slapping the ground, throwing rocks and can sometimes escalate to violence (Escribano, D. et al., 2022). Females often climb the social hierarchy in other ways e.g. formation of coalitions.
Lower ranking chimpanzees will perform more submissive behaviours e.g. soft panting, crouching/bowing, and grooming more dominant individuals. More dominant chimpanzees will often be more aggressive to lower ranking individuals. The behaviour of the “alpha” male and female will differ from all other members in the troop.
Population size example
Cinnabar moth lay on ragwort plants – hundreds of caterpillars can hatch on each plant resulting in cannibalism for survival, thus after pupation there is very little competition as harsh selection has already occurred. Hundreds of Cinnabar moth caterpillars (Tyria jacobaeae)can hatch on the same ragwort plant. This leads to competition over the scarce available food. Once there is no longer any food available, caterpillars will turn to cannibalism. After pupation, there is little to no competition for resources - the population is fitted to the carrying capacity.
Climate change impact on intraspecific competition
Drought and high temp. Resulting in reduced resources impacting and intensifying competition
Resulting in changes in feeding mating, flowering and migrational patterns
Can decrease competition in some areas – some species will thrive in milder climates allowing them to colonise previously uninhabitable areas with abundant resources
moving to higher altitudes will be necessary to find suitable climates
Adaptable generalists have the best chance of survival in this time of anthropogenic influences such as climate and land use change.
human assisted migration may be able to aid survival of species
Relocating species to suitable areas
Risk of being unable to compete/ unable to manage new abiotic factors
However, plant transport across latitudinal ranges may influence intraspecific competitive interactions of plants responding to different abiotic conditions.
Example: Blue bunch Wheatgrass -
It was found that the seeds collected from warmer locations were better adapted to higher temperatures and had a longer growing season. This allowed them to grow more quickly under resource stress and they reacted better to competition intra-specifically compared to the plants obtained from colder locations
Continual studies
Some species are mutualistic – if one is lost the other will also be subsequently
Effective to study species side by side for effective management and conservation
Intraspecific competition can have significant impacts on population levels, species proliferation and community dynamics. If ecologists can understand this, then they can better predict which way would be best to conserve and manage populations in the wild.
Continual studies are important for conservation and preventing extinction
What influences increase/ decrease in variation due to intraspecific competition?
Note that not all variation is a result of intraspecific competition.
Variation exists due to mutation etc. The environment dictates how this is selected.
How to avoid kin competition?
Kin recognition mechanisms help to reduce chance of this, in plants we can observe dispersal methods to prevent direct competition by growing directly alongside kin and this also occurs in many species which disperse as they become mature.
Kin on kin competition is intense in Cinnabar moths, R strategists by nature it is not an issue that offspring consume one-another as this selects for fitness and there are so many that genes will still get passed on in the surviving offspring.
In ants female workers are sterile daughters of the queen, in this relationship they protect their queen and only attack ants from foreign nests.
Some species maintain strong hierarchal levels such as hyenas preventing kin disputes.
In artificially low populations e.g. American wolves will individuals still compete in the same way?
Depends on the resource e.g. food competition may be lower whereas competition for mates in a small and dispersed population will be fierce. Territorial boundaries will be maintained and this is an issue if there is not enough available land for all individuals to maintain a suitable sized territory and this could result in increased territorial disputes along with negative interactions with humans
