Populations Flashcards
(26 cards)
Define population and give its key characteristics.
A population is a group of organisms of the same species, living in the same area (or habitat) at the same time.
Species Unity: All members belong to the same species, sharing genetic traits and exhibiting similar behavioral patterns.
Geographic Boundaries: Each population is confined to a defined area, such as a forest, lake, or island. These boundaries can be natural (e.g., a river) or artificial (e.g., a wildlife reserve).
Population Size and Density: The number of individuals within a population and their distribution across an area determine competition and resource availability.
Interactions: Members interact through mating, competition, cooperation, and communication, affecting their survival and reproductive success.
State what isolates populations of the same species.
Members of a population typically breed together, meaning reproductive isolation distinguishes one population of a species from another.
When multiple populations exist within a given area, they collectively form an ecological community.
Explain interaction within populations.*(intraspecific relationships)
Populations survive and adapt through two key types of interactions: competition and cooperation.
Competition: Individuals compete for limited resources such as food, water, space, or mates.
* Natural selection favors individuals with traits that improve their ability to secure resources, survive, and reproduce.
Cooperation:Members work together to improve survival chances, such as group hunting, communal defense, or cooperative parenting.
* Cooperation increases individual and group survival rates, strengthening the population as a whole.
State the reasons for estimating population size.
Practicality: Counting every individual is often impossible due to time, cost, and logistical constraints.
Conservation Efforts: Monitoring endangered species and evaluating the success of conservation strategies depend on accurate population size estimates.
Ecosystem Management: Understanding population sizes supports resource management, pest control, and predictions of ecological changes.
Define sampling error and state how it can be minimized.
Sampling error is the difference between the estimated population size and the true population size.
It arises because the sample only represents a subset of the population.
Ways to minimize sampling error:
Increase Sample Size: Larger samples generally lead to more accurate estimates.
Ensure Randomness: Avoid bias by using truly random sampling methods.
Consider Population Distribution: Populations with clumped distributions may require more samples for accurate estimates.
Explain quadrant sampling.
Quadrat sampling involves placing a square frame (a quadrat) at random locations within a habitat to sample a small section of the population.
The number of individuals within each quadrat is counted.
The process is repeated multiple times to gather a representative sample of the population.
Why use quadrant sampling for sessile species?
The population size or distribution of a non-motile (sessile) species can be determined using quadrat sampling.
A quadrat is a rectangular frame of known dimensions that can be used to establish population densities.
Quadrats are placed inside a defined area in either a random arrangement or according to a transect.
The number of individuals of a given species is either counted or estimated via percentage coverage.
Explain the use of standard diviation in quadrant sampling.
If the sampling process is repeated many times, a mean and standard deviation can be calculated.
The standard deviation shows the degree of data spread and could be used to indicate how evenly distributed the population is across the habitat.
Low Standard Deviation → Population is evenly spread across the habitat, making estimates more precise.
High Standard Deviation → Population is clumped in certain areas, requiring larger sample sizes for accuracy.
State reasons for using the method of capture- mark- release-recapture sampling to estimate the population of a motile organism.
For motile organisms—such as birds, fish, insects, and mammals—direct counting is impractical because they move constantly and can be difficult to track.
Ecologists use the capture–mark–release–recapture (CMR) method to estimate population sizes.
This method provides a statistically valid estimate of population size using a representative sample, allowing researchers to track species over time and assess conservation status, migration patterns, and population dynamics.
Describe the method of capture- mark- release-recapture sampling to estimate the population of a motile organism.
1. Capture:
A sample of the population is caught using traps, nets, or other capture techniques.
The number of captured individuals (M) is recorded.
2. Mark:
Each individual is marked in a harmless and recognizable way (e.g., colored bands for birds, non-toxic dye for insects, or electronic tags for mammals).
The mark must not affect survival, behavior, or make the animal more vulnerable to predator and be durable enough to remain until the next capture event.
3. Release:
The marked individuals are returned to their habitat and given time to mix back into the population.
4. Recapture:
After a set period, another sample of the population is captured. Scientists record how many marked vs. unmarked individuals are found.
Outline use of the Lincoln index to estimate population size from mark-recapture data.
The Lincoln index is a formula that provides a population size estimate based on three collected values:
Population size estimate = M × (N ÷ R)
M = the number of individuals caught and marked initially
N = the total number of individuals recaptured
R = the number of marked individuals recaptured
List assumptions made about the population when using mark-recapture methods to estimate population size.
That all individuals in a given area have an equal chance of being captured (sampling must be random)
That marked individuals will be randomly distributed after release (reintegration allows for an even spread)
That the action of marking individuals will not affect the mortality or natality of the population
That the marking will remain visible for the duration of the sampling process (not removed before recapture)
That the population size does not change significantly between the periods of first and second capture
Define carrying capacity.
Carrying capacity is the maximum population size that an ecosystem can sustain indefinitely without degrading the habitat.
* It depends on the availability of resources like food, water, and shelter.
* Changes in climate, natural disasters, and human activity can alter carrying capacity.
List examples of resources that may limit the carrying capacity of a population.
For Animals:
Food Supply – Herbivores compete for plants, while carnivores compete for prey.
Water Availability – Especially critical in deserts or during dry seasons.
Space & Territory – Needed for nesting, breeding, and hunting; territorial animals may fight over land.
Explain density dependent factors as an example of negative feedback control of population.
Population size can be impacted by density-dependent factors, which push populations back towards the carrying capacity.
Higher densities result in more competition and environmental resistance (limiting population growth), while low density populations can grow unimpeded.
This is an example of negative feedback, as increases in population density result in a reduction in population size.
Examples of density-dependent factors include (PANDA)
Predation, Access to habitat, Nutrient supply, Diseases, Added waste
Explain population growth curve.
Populations don’t grow indefinitely.
Over time, they follow a sigmoid growth curve, which consists of three distinct phases: rapid growth, slowed growth, and stabilization.
This curve explains how populations interact with their environment and the limits imposed by resources, competition, predators, and diseases.
State the phases of sigmoidal growth curve.
1. Exponenal Growth Phase
Initially, growth is slow as there are few individuals. As the numbers accumulate, there is rapid growth as natality rates exceed mortality.
2. Transional Phase
As the popula,on grows, resources eventually become limited, which leads to competiton. Mortality rates start to rise, slowing the growth.
3. Plateau Phase
When mortality rates equal the natality rate, the growth will become static. The population size will oscillate around a carrying capacity.
State the reasons for exponential growth in the initial phases.
- Resources are plentiful.
- There are few limiting factors like predators or diseases.
- The population is small, allowing rapid reproduction.
What factors affect population growth curves?
1. Predation
Impact: Predators control prey populations by hunting them.
Effect on Curve: The curve fluctuates as prey population declines, followed by predator decline, then recovery.’
2. Competition
Impact: Individuals compete for limited resources like food, water, and space.
Effect on Curve: Growth slows earlier, reducing the carrying capacity.
3. Disease
Impact: High population density makes it easier for diseases to spread, reducing population size.
Effect on Curve: Rapid decline during outbreaks, followed by stabilization as the population recovers.
Explain the S-shaped (sigmoid) growth curve.
Populations do not grow indefinitely. Instead, they follow an S-shaped (sigmoid) growth curve under natural conditions, which reflects the impact of resource availability, competition, and environmental limitations.
This curve shows how populations increase rapidly at first, slow as resources become limited, and eventually stabilize near the carrying capacity.
Outline cause and effect of competition in a population.
Causes
Limited Resources: Food, water, and shelter are finite, forcing individuals to compete.
Shared Needs: Members of the same species require the same resources, intensifying competition.
Carrying Capacity: Environments can only support a limited number of individuals.
Effects
Natural Selection: Traits that improve competitive success, like taller growth or stronger jaws, are passed on.
Population Regulation: Competition prevents populations from overusing resources, stabilizing ecosystems.
Evolutionary Pressure: Drives adaptations like faster growth rates or efficient resource use.
List examples of competition in intraspecific relationships.
Competition for Food
Lion Cubs: Young lions often compete for their mother’s milk or for access to prey carcasses.
Competition for Breeding Sites
Frogs: Males compete for territories with the best calling sites to attract females.
List examples of cooperation in intraspecific relationships.
Defense Against Predators
Fish Schools: Fish form tightly packed bait balls to confuse predators and reduce individual risk.
Cooperative Hunting
Lions: Work together to hunt zebras or buffalo, taking down prey too large for one lion alone.
Explain the typical dynamic equilibrium of populations of predator and prey.
1. Prey Population Increases → Predator Population Grows
More prey means more food availability for predators.
Predator survival rates improve, and their population increases.
2. Predator Population Increases → Prey Population Declines
As predators consume more prey, prey numbers fall.
This reduces food availability for predators.
3. Prey Population Declines → Predator Population Declines
Fewer prey leads to food shortages for predators.
Starvation and reduced reproduction cause predator numbers to drop.
4. Predator Population Declines → Prey Population Recovers
With fewer predators, prey populations rebound.
This restarts the predator-prey cycle.
