Intraspecific Interactions Flashcards
Why is it unlikely for populations to undergo exponential growth?
populations cannot grow indefinitely as other interactions occur to curb growth. - these come in many forms i.e. disease, competetion. Populations do not have unlimited resources and will reach the carrying capacity of the habitat Population size has a negative linear feedback.
What is an example of intergeneratial interactions?
The saw-toothed grain beetle - the female lays 100 eggs over a year, there are egg. larval, pupal and adault stages. The resources exploited are often temporary. Adults impose a negative density dependent feedback - increased caniballism on immature beetles.
Explain density dependance
Populations do not have unlimited resources, and there is a carrying capacity to the ecosystem. Therefore the population size has negative linear feedback.
What is an example of a time lag?
Blowflies: When the adult population is high there are more eggs/larvae produced than can be supported by resources to pupation. As a result no adults are produced in this time period and the adult population gradually declines and hence fewer eggs are laid. The intensity of larval competition is decreased and so an increased proportion of the larvae successfully pupate - the adult fly population increases. i.e. density dependence does not directly effect adult stage it is mediated through larval food availability.
What is an example of intergenerational interactions?
Chick compete for food - leads to a weight hierarchy. this has implications for survival, condition at fledging and subsequent recruitment. It also has implications for adults in terms of provisioning and productivity as larger broods cost more. E.g. when food is scarce kittiwakes eject smaller siblings.
What is an allee effect?
A positive association between absolute average individual fitness and population size over some fixed interval. e.g. breeding success correlated with density, anti-predator effect, more synchronous laying in denser colonies. Cooperative behaviour.
What are sex-ratios?
There are male-based sex ratios in many bird species, especially those with small populations. This arises from sex differences in survival, recruitment or dispersal. E.g. Higher reproductive costs, predation risk on the nest, stringer conspecific attraction - there are fewer females at poor sites, sex-dependent migration patterns.
What is an example of the effects of sex-ratios?
KAKAPO: critically endangered - 3:2 male sex bias.
Intra-sex interaction? Within sexes.
Models assume that resources are available equally. Age-structure has been introduced but need to consider sex-structure as well. There is variation within sexes in access to resources. e.g. male dung beetles - horn production not heritable it is dictated by resource availability at larval stage. Males guard tunnels where females lay eggs. Males with larger horns win fights. However smaller males can dig side tunnels - having no horn is advantageous.
Inter-sex interactions? Between sexes.
Typically female choose their preferred mate. This structures populations and determines the direction of population growth. i.e. females prefer more elaborate calls, males often respond to female presence by elaborating their display as adding complexity increases attractiveness but also increases predation risk.
overview of intraspecific interactions
Logisitic growth models need to account for:
- intra and intergenerational interactions e.g. sibling rivalry and sawtoothed beetle
- Timelags e.g. blowfly
- Non-linear relationship between birth, death and numbers
- sex-ratio (e.g. kakapo)
- intra and inter-sex interactions e.g. influence of mate choice.
What is life-history theory?
Trade-offs exist between life-history components i.e. resources allocated to competing activities (e.g. reproduction, survival) to maximise lifetime fitness. e.g. a decrease in current fecundity may allow for future survival.
What is a deterministic model?
A model where the vital rates i.e. Birth, death immigration, emigration are constant over time although they might vary between age/stage/sex structure. There is an exact outcome - the same result for every reiteration of the model.
What is a stochastic model?
As natural systems include stochastic processes, these models include the chance events which can influence long-term dynamics. Population parameters vary with a frequency distribution and mean and SE. The model takes a sample parameter from this distribution and so future estimates are a possible range of values.
What is a catastrophic event?
one of a number of external factors that reduces population size e.g. drought, floods, fire. For example the Galapagos finch underwent a severe decrease in abundance after drought in 1977 that reduced seed abundance.
