Population Dynamics 5

What are r-selected species?

• a fast-growing and reproducing species, often the first to take up unused resources and living space

• early colonisers in disturbed environments

• known as opportunists

What is the life strategies of r-selected species?

• species have a high birth rate

• population explodes and reaches maximum reproductive potential of the species

• then population declines or crashes in numbers

• replaced by competitors during rapid decline

• to survive, they must:

  • colonise new environments quickly

  • be able to reproduce rapidly in large numbers

What are the features of r-selected species?

• smaller in size

• have short life cycles

• lack of parental care for young

What are K-selected species?

a slow-growing, long-lived species typical of those in a long-established biological community

What is the life strategy of K-selected species?

• slow and steady’ life strategy

  • organisms reproduce at a slower rate (lower birth rate)

  • high level of parental care

  • offspring survival rate is much higher

What are the features of K-selected species?

• larger in size

• longer-lived species

• fewer offspring

• outcompete r-selected species

• steadier population growth pattern

• population numbers exist close to carrying capacity of environment

What is carrying capacity and what is it determined by?

• the maximum population size of a species that can be supported in an environment with limited resources

• as population density increases, competition increases

• determined by:

  • the amount of resources (e.g. food, water)

  • predation

  • disease

  • competition between species (interspecific/intraspecific competition)

What are the different phases in population growth curves?

• lag phase

• exponential phase

• transitional phase

• plateau/stationary phase

Describe the lag phase.

• population growth is slow

• due to having few mating partners and they may be very widely dispersed in the environment

Describe the exponential phase.

• high population growth

• birth rate exceeds death rate

• due to abundance of resources

• maximum growth rate occurring under optimal conditions

• no environmental resistance

  • environmental resistance - refers to environmental factors that hinder population growth (e.g. competition)

Describe the transitional phase.

• population growth slows as environmental resistances has reached

• increased competition for space, food, and mating partners

• death rate increases and/or birth rate decreases

Describe the plateau/stationary phase.

• carrying capacity (K) has reached

• population has reached equilibrium

• birth rate is roughly the same as death rate

• limiting factors keep the population stable

• fluctuations occur due to slight changes in birth rate and death rate

What are density-independent factors? Give examples.

• environmental factors that occur not due to the size or density of a population

• e.g.:

  • soil salinity

  • humidity

  • natural disasters

  • amount of rainfall

What are density-dependent factors? Give examples.

• environmental factors that occur due to increase or decrease in population size and density

• e.g.:

  • competition

  • disease

  • parasites

  • predation

  • food supply

Open vs closed ecosystems?

• open ecosystem - migration occurs freely in response to environmental changes

• closed ecosystem - migration does not occur but births and deaths still impact population size

Immigration vs emigration?

• immigration = entering/moving to a new ecosystem/region

• emigration = leaving an ecosystem/region

What is the population growth rate formula?

population growth rate = (birth rate + immigration rate) - (death rate + emigration rate)

What is direct observation in terms of measuring abundance?

• sighting & counting

• e.g. The Great Cocky Count

  • citizen survey count

What are quadrats?

• a square, rectangular frame of convenient (appropriate) size used to mark out an area in which the vegetation is sampled

  • larger fields require larger quadrats and vice versa → gives a more precise estimate

  • e.g. 50x50cm for a backyard, 1-2m squares for medium-sized fields

• used to estimate population size, population density, diversity

• used on for immobile/sessile species

• organism size, distribution & area are considered before deciding on quadrat size

• placed randomly in the area to be studied without bias (quadrat throw)

  • if the centre of the species does not fall inside the quadrat, don’t count

How are quadrat throws beneficial?

• the more quadrats that are thrown, the more accurate your estimate of population size/population density for a chosen species would be

• if sufficient quadrats are chosen, your calculations would be representations of the area

What is quadrat sampling and its formula?

• estimating population size and density using quadrats

  1. know the total area of area you are studying

  2. randomly select the quadrats to use for counting for a species you are estimating

  3. record the data for each quadrat in your book

What is a transect?

• line drawn through a community

• information is gathered from along the line and used to estimate the distribution of species within that community

• quadrats may be placed at intervals along the transect line to improve the data collected as data on density in specific locations may also be recorded

• it is best to use the line transet method if environmental factors (e.g. soil type/soil pH/ soil salinity) change along the distance to be sampled

Why is the combination of using quadrats and line transects the best?

• provides a full picture of population distribution and species abundance patterns in environments

• data gathered using transects offers fairly accurate information regarding distribution of individuals and/or species

• quadrats offer a comprehensive picture of species abundance but not distribution

Describe the process of capture-mark-recapture.

1. capture

   • animals are caught randomly without being hurt

   • small animals are trapped in cages/pitfalls in the ground, birds are trapped in fine nets

   • flying insects are attracted to light traps

2. mark (tag) and release

   • each capture animal is released so it is not obvious to predators/harmful to the organism

   • insects are usually marked with a small blob of paint, whereas birds are marked on the leg/wing

   • the animals are then returned to their habitat to allow them to re-disperse/mix back into the original population for some time

3. recapture

   • a random sample is taken from the whole population and the number of marked individuals in it is then counted

   • the timing of recapture needs to allow for the capture of a random mixture of individuals, but without leaving it so long that many of the original marked individuals have died

   • the number of marked organisms and the total number of organisms in the second capture is also recorded

What is the capture-mark-recapture formula?