Population Basics
What is a population?
A group of individuals of the same species living in the same area at the same time.
What type of growth produces a J-shaped curve?
Exponential growth.
Name one density-dependent limiting factor.
Competition, predation, disease, or parasitism.
In a predator-prey relationship, what does the predator eat?
The prey
If a population starts at 500 individuals and gains 50 individuals, what is its new population size?
550 individuals
What is population density?
The number of individuals of a population per unit of area or volume.
What type of growth produces an S-shaped curve?
Logistic growth.
Name one density-independent limiting factor.
Flood, drought, wildfire, extreme temperatures, or another environmental disturbance.
If the prey population increases, what might eventually happen to the predator population?
The predator population may increase because more food is available.
A population of 1 000 individuals increases by 10%. How many individuals are added?
100 individuals
What is carrying capacity?
The maximum population size that an environment can sustainably support based on available resources and environmental conditions.
What is the major difference between exponential and logistic growth?
Exponential growth assumes unlimited resources and continues increasing rapidly, while logistic growth slows as the population approaches carrying capacity.
Why is predation considered density-dependent?
Its effect can become stronger as prey population density increases because predators have greater opportunities to encounter prey.
Why does the predator population typically lag behind the prey population?
Predators need time to respond reproductively to increased food availability, so their population increases after the prey population increases.
Using the exponential growth model Nt=N0(1+r)t calculate the population after one year if N0=2 000 and r=0.05.
2 100 individuals
What is fecundity?
The reproductive capacity or potential of an organism/population.
A population is increasing rapidly but begins to level off. Which growth model best describes it? Explain.
Logistic growth because growth slows as the population approaches carrying capacity.
A drought reduces the amount of water available to a population regardless of how many individuals are present. Is this density-dependent or density-independent?
Density-independent.
If the predator population suddenly increases, what would you predict will happen to the prey population?
The prey population may decrease because predation pressure increases.
A population of 5,000 grows at 4% annually. Calculate its predicted population after two years using the exponential growth model.
Nt= 5 000(1.04)2
Nt= 5 408 individuals
Explain why carrying capacity is not necessarily a fixed number.
It can change when environmental conditions and resource availability change, such as changes in food, water, habitat, disease, or climate.
Why is exponential growth unlikely to continue indefinitely in a real ecosystem?
Resources and space are limited, and factors such as competition, predation, disease, and environmental conditions limit population growth.
A population grows beyond the environment's carrying capacity. Predict what might happen next.
Resources may become depleted, competition may increase, mortality may rise, and the population may decline toward or fluctuate around carrying capacity.
Explain why predator and prey populations may cycle rather than remain constant.
Changes in prey abundance affect predator abundance, and changes in predator abundance then affect prey abundance. This creates repeated fluctuations between the populations.
A population has a starting size of 10 000 and a growth rate of 8%. Its habitat has a carrying capacity of 12 000. Why would an exponential model eventually become unrealistic?
Exponential growth assumes unlimited resources and would eventually predict a population larger than the environment can support. The carrying capacity would limit further sustainable growth.