Population Ecology Flashcards
3.2.13 Use the Lincoln index to estimate the population size from secondary or primary data.
What is the Lincoln index and what does it estimate?
The Lincoln Index is used to estimate the size of a population of mobile animals. It uses the sampling method called Capture-Recapture.
The formula is N = Mn/m
Where:
M = number of individuals caught, marked and released initially
n = number of individuals caught on second sampling
m = number of individuals recaptured that were marked
3.2.13 Use the Lincoln index to estimate the population size from secondary or primary data.
Greensapce wants to determine the number of polar bears left in the wild. They capture 6 polar bears and then release with a microship inserted into their leg. A month later they catch 30 polar bears, and 2 of those have a microchip.
Estimate the total polar bear population.
N = 6 x 30/ 2
= 90 polar bears
3.2.12 Calculate population growth rate and change (using birth, death, immigration, and emigration data)
What four factors is a population size effected by? Hence, how is change in a population calculated?
Natality (births by germination)
Mortality (deaths)
Immigration (organisms moving in from outside the population)
Emmigration (organisms moving out of the population)
Hence
Change in population = (Births + Immigration) - (Deaths + Emigration)
3.2.12 Calculate population growth rate and change (using birth, death, immigration, and emigration data)
Recall how to calculate percentage change in a population.
% chnage in population = (final population - initial population) / initial population x 100
3.2.12 Calculate population growth rate and change (using birth, death, immigration, and emigration data)
Calculate rate of change in population size
To calculate an annual rate of change, divide the total change by the amount of time. When populations decrease in size over time, the rate of change will be a negative value.
Populations can grow in two distinct patterns:
Exponential growth J-curve
Logistic growth S-curve
3.2.14 Ananlyse population growth data to determine the mode (exponential growth J-curve, logistic growth S-curve) of population growth
When does the exponential growth J curve occur?
-When births > deaths
-In species that have a short generation time and give rise to large numbers of offspring. For example, bacteria, weed species and insects
-Generally occurs only for relatively short periods
-Normally for some species of plants/animals when conditions are favourable. For example, salvnia fern (introduced species) free-floating aquatic weed - in right conditions, its population can double every 2-5 days. Can form a dense mat on top of waterways amd block sunlight from other equatic plant life.
-Leads to “boom and bust” after resources are depleted
3.2.14 Ananlyse population growth data to determine the mode (exponential growth J-curve, logistic growth S-curve) of population growth
When does the logistic S curve occur?
In ecosystems, population growth is effected by density-dependent factors such as competition for resources.
When a population reaches equilibrium and becomes relatively constant the number of births and deaths cancel each other out, as the species has reached the maximum size that the ecosystem can support. This is called the carrying capacity for that species.
Generally there is exponential growth which then flattens out as it begins to be effected by density-dependent factors. POpulation growth declines until births = deaths
3.2.14 Ananlyse population growth data to determine the mode (exponential growth J-curve, logistic growth S-curve) of population growth
What are the phases of the growth curves?
Exponential growth:
-Total number of individuals increases as the number of reproducing females in the population increases
- Initially the growth is slow due to a small population size
Logistic growth:
-Populations are dependent upon finite resources for survival
- This will limit the exponential growth phase of a population curve
- There is a lag phase, exponential growth, deceleration phase and equilibrium phase which is when the total number of individuals that the environment can hold is reached
3.2.14 Ananlyse population growth data to determine the mode (exponential growth J-curve, logistic growth S-curve) of population growth
Describe the shape of the equilibrium phase as occurring in nature.
In nature, the population usually fluctuates above and below the carrying capacity level over time.
3.2.14 Ananlyse population growth data to determine the mode (exponential growth J-curve, logistic growth S-curve) of population growth
The carrying capacity of an ecosystem refers to the:
size of population that can be indefinitely supported on the availiable resources and services of that ecosystem
3.2.10 Define the term carrying capacity
In Biology, the carrying capacity is the size of the population that can be supported indefinitely on the available resources and services of that ecosystem.
3.2.11 Explain why the carrying capacity of a population is determined by limiting factors (biotic and abiotic).
3.2.15 Discuss the effect of changes within population-limiting factors on the carrying capacity of the ecosystem
What are the factors that affect population size?
Density dependent factors
Predators
Availiability of resources (e.g. shelter, food, and water)
Nutrient supply (i.e. food source)
Disease/ pathogenic speed
Accumalation of waste
Density independent factors
Phenomena (e.g. natural disasters)
Abiotic factors (e.g. temperature, CO2 levels)
Weather conditions (e.g. floods, storms, etc)
3.2.11 Explain why the carrying capacity of a population is determined by limiting factors (biotic and abiotic).
Limiting factors within every ecosystem, such as the availability of food or the effects of predation and disease, prevent a population from becoming too large. These limiting factors determine an ecosystem’s carrying capacity, or maximum population size the environment can support given all available resources. Carrying capacities can change. An ecosystem’s carrying capacity may fluctuate based on seasonal changes, or it may change as a result of human activity or a natural disaster. For example, if a fire destroys many trees in a forest ecosystem, the forest’s carrying capacity for tree-nesting birds will decrease.
OR
Limiting factors determine carrying capacity. The availability of abiotic factors (such as water, oxygen, and space) and biotic factors (such as food) dictates how many organisms can live in an ecosystem. If abiotic or biotic factors change, the carrying capacity changes as well. Natural disasters can destroy resources in an ecosystem. If resources are destroyed, the ecosystem will not be able to support a large population. This causes the carrying capacity to decrease. If a population exceeds carrying capacity, the ecosystem may become unsuitable for the species to survive. If the population exceeds the carrying capacity for a long period of time, resources m ay be completely depleted. Populations may die off if all of the resources are exhausted.
3.2.15 Discuss the effect of changes within population-limiting factors on the carrying capacity of the ecosystem
Discuss the effect of predators on the carrying capacity of the ecosystem.
If the density of prey increases, predators will have more access to this food and their population will increase. This redurces the population of the prey species. As the number of prey falls, intraspecific competition will reduce the predator population size. Therefore too many predators and not enough prey leads to predators starving and dying because they can’t find enough food. Thus both availability of resources and predation pressure affect the size of prey populations.
3.2.15 Discuss the effect of changes within population-limiting factors on the carrying capacity of the ecosystem
Discuss the effect of predators on the carrying capacity of the ecosystem.
When resources such as shelter, water and mates are in low supply, individual organisms must compete. Competition occurs when two organisms require the same resources that are in limited supply. Competition for resources like food and space cause the growth rate to stop increasing, so the population levels off. This flat upper line on a growth curve is the carrying capacity.
