Lecture 24/25

Lecture 24 - Population and Community Ecology

Q: What is an individual in ecology? Give an example.
A: A single organism. Example: One deer.

Q: What is a population? Give an example.
A: A group of the same species living in one area. Example: A herd of deer.

Q: What is a community? Give an example.
A: All species in one area interacting. Example: Deer, wolves, and trees in a forest.

Q: What is an ecosystem? Give an example.
A: A community plus its non-living environment. Example: Forest with soil, water, and animals.

Q: What characteristics can be studied about a population?
A:

  • Size: Number of individuals.

  • Density: Individuals per area.

  • Distribution: How individuals are spread out.

  • Growth rate: How fast the population changes.

Q: What are r-selected (opportunistic) species?
A: Species with high reproduction rates, short lifespans, and rapid growth. Example: Insects.

Q: What are k-selected (equilibrial) species?
A: Species with low reproduction rates, long lifespans, and stable populations. Example: Elephants.

Q: What increases population size? Which has a bigger effect?
A:

  • Births and immigration.

  • Births usually have a bigger effect.

Q: What decreases population size? Which has a bigger effect?
A:

  • Deaths and emigration.

  • Deaths usually have a bigger effect.

Q: What is the equation for population growth?
A: ΔN/Δt=rN\Delta N / \Delta t = rNΔN/Δt=rN, where ΔN\Delta NΔN is the population change, rrr is the growth rate, and NNN is the population size.

Q: What is rrr? How is it calculated?
A:

  • rrr is the growth rate.

  • Calculated as (birthrate−deathrate)/population(birth rate - death rate) / population(birthrate−deathrate)/population.

  • r=0r = 0r=0: No growth.

  • r>0r > 0r>0: Population grows.

  • r<0r < 0r<0: Population shrinks.

Q: What is KKK?
A:

  • KKK is carrying capacity: the maximum population the environment can support.

  • Determined by available resources.

Q: What is density-dependent environmental resistance? Examples?
A: Factors that worsen with population size. Example: Food shortages, disease.

Q: What is density-independent environmental resistance? Examples?
A: Factors that affect populations regardless of size. Example: Natural disasters, weather.

Q: What are the two population growth models?
A:

  1. Exponential: Rapid growth (J-shaped curve).

  2. Logistic: Growth slows as it nears KKK (S-shaped curve).

Q: What are the types of interspecific interactions? Symbols?
A:

  • Mutualism (+/+): Both benefit. Example: Bees and flowers.

  • Competition (-/-): Both harmed. Example: Two species competing for food.

  • Predation (+/-): One benefits, one harmed. Example: Lion and zebra.

  • Parasitism (+/-): One benefits, one harmed. Example: Tick on a dog.

  • Commensalism (+/0): One benefits, the other unaffected. Example: Bird nesting in a tree.

Q: What is competitive exclusion?
A: When one species outcompetes another, driving it out.

Q: What is resource partitioning?
A: When species divide resources to reduce competition.

Q: How can community interactions lead to coevolution? Example?
A:

  • Species evolve in response to each other.

  • Example: Flowers evolving for specific pollinators.

Lecture 25 - Ecosystem Ecology

Q: What is an ecosystem?
A: A community of living and non-living things interacting.

Q: Why are there more producers than consumers?
A: Energy is lost at each trophic level (about 90%), so fewer consumers can be supported.

Q: What is a biogeochemical cycle?
A: The movement of elements like water, carbon, and nitrogen through living and non-living parts of ecosystems.

Q: Why are water, carbon, and nitrogen important?
A: They are essential for processes like hydration, photosynthesis, and protein synthesis.

Q: How does human industry affect the carbon cycle?
A:

  • Adds CO2 through burning fossil fuels.

  • Leads to increased atmospheric carbon.

Q: What are the impacts of rising atmospheric carbon levels?
A:

  • Climate change, ocean acidification, and habitat loss.

Q: How can carbon emissions be reduced?
A:

  • Planting trees, reducing fossil fuel use, and using renewable energy.

Q: How do organisms like plants and animals get nitrogen?
A:

  • Plants absorb it from soil as nitrates.

  • Animals eat plants or other animals.

Q: What organisms convert atmospheric nitrogen into usable forms?
A: Nitrogen-fixing bacteria in soil or plant roots.