Ecology 4 - Flashcards
Explain shortage of food and populations
- Limited resources
- Shortages of fod and shelter,increased competition between individuals and disease outbreaks, will eventually cause growth to slow down
Explain logistic growth
- Results when the environment restricts growth
- Usually occurs in organisms with continuous breeding
- Produces an S-shaped or sigmoidal curve
Explain the four phases of logistic growth
- Lagphase - Growth is slow as the population is still small ( bottom )
- Exponential growth phase – Growth increases as more individuals are added
- Deceleration phase–Growth slows down
- Stable equilibrium phase–Very little growth ( top )
Explain carrying capacity
- ” K “ of a population is the maximum number of individuals that can be supported by the environment
- Population growth cannot increase indefinitely because resources are limited
- When a population reaches carrying capacity, it stops growing – the death rate matches the birth rate
What happens at the carrying capacity
The population will usually fluctuate around the carrying capacity
Explaing logistic growth formula with carrying capacity
- Calculate logistic population growth
The formula becomes:
G = rmaxN ((K-N) / K)
- G = change in population size
- rmax = maximum net reproduction per individual
- N = population size
- K = carrying capacity
Explain logistic growth fully
- (K-N) / K represents the effect of carrying capacity on population growth
- If N is small, the term (K-N) / K is close to one and has little effect on population growth
- If N is approaching K, the term (K-N) / K is close to zero and has a strong effect on population growth
Explain population regulation and its factors
- Population regulation is the control of population size
- Population regulating factors (limiting factors) limit the size of a population
- Prevent a population from increasing exponentially
What factors play a role in regulating population size
Both biotic and abiotic factors
What are the factors of population size regulation
- Density-independent factors (abiotic)
- Density-dependent factors (biotic)
- Intrinsic factors (biotic)
For competition to take place what ,ust there be
- Resources in limited supply
- Incr in density ( leading to reduction in fitness )
Explain density independent factors
- A population regulating factor which is not influenced by the population size
- The intensity of the effect does not increase with increased population size
Examples: severe weather conditions, fires, natural disasters
Explain density dependent factors
- A population regulating factor which is influenced by population size
- The percentage of the population affected does increase as the density increases
Examples: predation, competition, disease, parasites
Explain competition
- When individuals compete for resources (e.g. food, light, space) that are in limited supply
- As a result, some members of the population may be unable to survive, grow, or reproduce
Explain intraspecific competition
Individuals of the same species compete with each other
Explain interspecific competition
Individuals of one species compete with individuals of another species
Explain intrinsic factors
- Factors based on anatomy, physiology, behaviour) may also help to regulate population size
- Density-independent and some density- dependent factors are extrinsic
eg ) Territoriality and Dominance hierarchies
What are examples of intrinsic factors
- Dispersal – leaving the population
- Social behaviour – co-operation and sharing of resources
- Physical characteristics – adaptations to the environment
Explain strategies for survival
- Evolution acts on organisms to increase their individual genetic contributions to future generations
- To grow, survive, reproduce and thus contribute genetically to future generations, organisms must allocate their limited energy supply for maximum benefit
Explain life history
- Concerns lifelong patterns of growth and reproduction and includes particulars such as:
- Number of births per reproduction
- Age at reproduction
- Life span
- Probability of living the entire lifespan
- Natural selection shapes the life history of a species to suit its environment
Explain the two life history strategies
- r-selection
- In unpredictable environments, density- independent factors keep populations in the lag or exponential phase of growth - K-selection
- Stable environments allow populations to approach the carrying capacity
Explain r-selection fully
- Organisms live in unstable, unpredictable environments
- They are subject to density-independent factors
- They need to reproduce quickly, before the environment changes
- Produce many “cheap” offspring
- r-Selected organisms are called r-strategists
What are characteristics of r-strategiests
- Low population density
- Produce large numbers of offspring
- Small body size
- Early maturity
- Short-lived
- No parental care
- Controlled by density-independent factors Good dispersers and colonizers
Explain k-selection fully
- Organisms live in stable, predictable environments
- The population is at or near the carrying capacity
- Organisms are subject to density-dependent factors
- Produce few “expensive” offspring
- K-selected organisms are called K-strategists
What are characteristics of k-strategists
- High population density
- Produce small numbers of offspring
- Large body size
- Late maturity
- Long-lived
- Significant parental care
- Controlled by density-dependent factors
- Specialists
