Unit 11- Ecology

Define a population

A group of organisms of the same species living in the same area at the same time.

What is a sample and why is sampling used

A sample is a subset of a population; sampling estimates population size or characteristics without studying every individual.

What is sampling error and how can it be reduced

Sampling error is the difference between a sample estimate and the true population value; random sampling and larger sample sizes reduce bias and variation.

Why is randomness important in sampling

It gives each area or individual an equal chance of selection and reduces sampling bias.

How are sessile and motile organisms sampled

Sessile organisms are sampled using quadrats or transects; motile organisms are commonly sampled using capture-mark-release-recapture.

How is quadrat sampling used to estimate a population

Randomly place quadrats

How is capture-mark-release-recapture used to estimate population size

Capture and mark individuals

What assumptions are made in mark-recapture sampling

The population is closed; marks remain visible; marking does not affect survival or behavior; marked individuals mix randomly; individuals have equal capture probability.

What is the Lincoln index

Estimated population = (number initially captured × total individuals recaptured) ÷ number of marked individuals recaptured.

What is carrying capacity

The maximum population size an environment can sustainably support.

What factors can limit carrying capacity

Food

How does negative feedback control population size

Increasing population density increases limiting factors

What is the difference between density-dependent and density-independent factors

Density-dependent factors become stronger as population density increases; density-independent factors affect populations regardless of density.

What are examples of density-dependent factors

Competition

What are examples of density-independent factors

Drought

Why do organisms produce more offspring than the environment can support

Producing many offspring increases the chance that some survive and reproduce despite environmental pressures.

When can exponential population growth occur

When resources are abundant

How does a sigmoid population growth curve develop

Population initially grows exponentially; competition and resource limitation increase

How do exponential and sigmoid growth curves differ

Exponential growth is J-shaped and occurs with few limiting factors; sigmoid growth is S-shaped and levels off at carrying capacity.

Why is a logarithmic scale useful for population graphs

It allows very large changes in population size to be displayed on the same graph and makes exponential growth easier to compare.

How can yeast or duckweed population growth be monitored

Measure population size at regular time intervals under controlled conditions and plot population size against time.

How can observed and expected population growth be compared

Plot the observed data and compare it with predicted exponential or sigmoid growth; deviations indicate environmental limitations.

What is an intraspecific relationship

An interaction between individuals of the same species.

What causes intraspecific competition and what are its effects

Limited resources cause competition

What is cooperation and what are its benefits

Individuals work together to improve survival or reproduction

What is the typical predator-prey population cycle

An increase in prey provides more food

Give an example of predator-prey oscillation

Hare populations increase

What is a community

All populations of different species living and interacting in the same area.

What are the major types of interactions in a community

Mutualism (++)

What are examples of major community interactions

Mutualism: coral and zooxanthellae; competition: plants for light; predation: lion and zebra; herbivory: caterpillar and plant; parasitism: tapeworm and human.

What is the mutualistic relationship between Fabaceae and Rhizobium

Rhizobium fixes atmospheric nitrogen into usable compounds; the plant provides carbohydrates and a protected root-nodule habitat.

What is the mutualistic relationship between orchids and mycorrhizal fungi

Fungi increase mineral and water absorption; the orchid provides carbohydrates to the fungi.

What is the mutualistic relationship between hard corals and zooxanthellae

Zooxanthellae provide photosynthetic products; coral provides shelter

What are endemic and invasive species

Endemic species are native and restricted to a particular area; invasive species are non-native species that spread and cause ecological harm.

How can an invasive species affect the realized niche of an endemic species

Competition from the invasive species can restrict the resources available to the endemic species

How can invasive and endemic species compete

They may compete for food

How can a chi-square test investigate interspecific competition

Record presence or absence of two species at multiple sites

What are the null and alternative hypotheses for a chi-square test of association

H₀: species presence is independent; H₁: species presence is associated.

How are expected frequencies calculated in a chi-square contingency table

Expected frequency = (row total × column total) ÷ grand total.

What is the chi-square formula

χ² = Σ((observed − expected)² ÷ expected).

Why can’t a chi-square association alone prove competition

Other environmental factors may cause the observed association

How can direct experimentation test for interspecific competition

Manipulate the presence or abundance of one species while controlling other variables

What is top-down control

Population regulation caused primarily by consumers such as predators.

What is bottom-up control

Population regulation caused primarily by resource availability such as nutrients

What is allelopathy

Chemical inhibition of one organism by chemicals released by another organism.

Give an example of allelopathy

Black walnut trees release juglone

What are antibiotics

Chemicals produced by microorganisms that inhibit or kill other microorganisms.

Give an example of natural antibiotic production

Penicillium produces penicillin

What is a habitat

The environment in which an organism normally lives.

What factors describe a habitat

Abiotic conditions

What is an adaptation

An inherited characteristic that increases an organism’s ability to survive and reproduce in its environment.