L10 - Species Interactions and Community Dynamics Flashcards
Conditions
physical or chemical characteristics of the environment; not consumed by the organism
Resources
availability regulated by the environment; consumed by the organism,
E.g. mineral nutrients, light, water
Liebig’s Law of the minimum
the limiting resource determines maximum growth
If one essential nutrient is deficient, plant growth will be poor even when other nutrients are abundant.
What determines fundamental niche?
Species have an optimum and tolerance range for conditions and resource availability. The combination of these determines where a species can exist.
Populations
group of individuals of the same species occupying a space at the same time (n)
What are populations characterised by?
Density, age structure (distribution of individuals over age classes), birth rate and death rate.
What does population growth (r) depend on?
Age distribution, survivorship and fertility per age class. Would be exponential J shaped if no limiting resources and competition (is S shaped instead).
Carrying capacity (K)
refers to the number of individuals that can be supported in a given area within natural resource limits and sustainably (i.e. without degrading the natural, social, cultural and economic environment)
Not fixed for a given area
Intraspecific competition
competition within a species
interspecific competition
competition between species
Competition coefficient
the ratio between the competitive effects of both species (1/10 = 0.1)
Total competitive effect
= (competition coefficient)(total population size)
How is growth determined without competition?
By the fraction of the carrying capacity that is used by the population
Dominant competition
if a species can deplete the resource beyond K of the other species, without surpassing its own K
Multiple outcomes
if each species can reduce the resource beyond the other species K, without affecting its own growth
Coexistence
if neither species can exclude the other by reducing the resource beyond K
Gause’s law
species with identical ecological requirements cannot coexist in the same environment
Competitive exclusion rarely occurs in nature because?
- Variability in resource availability
- Competition for multiple resources at the same time
- Diffuse competition (multiple species)
- Resource partitioning and adaptation - niche differentiation
Diffuse competition
the total (weak) competitive effects of several interspecific competitors
Niche differentiation
process by which competing species or individuals adjust their resource use or behaviour to minimise direct competition
How do species change in response to competition?
Change behaviour or morphological characteristics (e.g. plants can change height, stem diameter etc)
Why do populations fluctuate around K?
Time lags
Exploitative (or scramble) competition
organisms only react to the resource, not each other. Shared resources are overused and depleted due (tragedy of the commons)
Contest (or interreference) competition
organisms actively compete with each other over the resource. There are winners and losers.
What is the most probable shaped curve for population growth?
S curve, this reflects how growth is not exponential due to limiting factors. Instead it levels off at carrying capacity
What causes niche differentiation?
Niche shifts = determined by the replacement of niche space between species (i.e. change location)
Niche contraction/expansion = species reduces/increased its niche breadth (i.e. behaviour)
