Energy Flow
Define the term "primary producer" and give one example
Primary producer: an organism that produces organic compounds from inorganic sources (autotroph).
What is a food web, and how does it differ from a food chain?
Food web: interconnected network of food chains showing multiple feeding relationships. Food chain: linear sequence of who eats whom.
Define mutualism and give one real-world example
Mutualism: both species benefit. Example: pollinators (bees) and flowering plants.
Define population density.
Population density: number of individuals per unit area or volume.
Name one human activity that directly reduces biodiversity.
Example: deforestation, overfishing, pollution, urbanization.
Explain why only about 10% of energy is typically transferred from one trophic level to the next.
About 10% is transferred because most energy is used for organisms' metabolism, lost as heat, or left unconsumed; only a small fraction is converted into biomass available to the next trophic level.
Define "abiotic factor" and give two examples that influence an ecosystem.
Abiotic factor: nonliving environmental factor (e.g., temperature, sunlight, soil pH, water availability).
Describe commensalism and provide an example.
Commensalism: one benefits, the other unaffected. Example: epiphytic orchids growing on trees.
What is carrying capacity (K), and what major factors determine it in an ecosystem?
Carrying capacity (K): maximum number of individuals an environment can sustainably support. Determined by resource availability, habitat space, predation, disease, and abiotic conditions.
Explain how habitat fragmentation can affect population gene flow
Fragmentation isolates populations, reducing migration and gene flow, increasing inbreeding and reducing genetic diversity.
Identify two ways energy is lost as it moves through a food chain.
Energy lost as: heat from respiration, movement/maintenance, indigestible parts (waste), and through incomplete consumption.
Explain the concept of ecological niche and how it differs from habitat.
Niche: the role and resource use of a species (including interactions, conditions tolerated); habitat: the physical place where a species lives.
Explain the term "predator-prey dynamics" and one way these dynamics can affect population size
Predator-prey dynamics: predators consume prey affecting prey numbers; increases in predators can reduce prey, and prey abundance can limit predator populations.
Sketch verbally (describe) the four phases of a typical logistic growth curve and name which phase shows fastest population growth.
Logistic growth phases: lag (slow start), exponential (rapid growth), deceleration (growth slows as resources limit), stationary (population fluctuates near K). Fastest growth: exponential phase.
Describe one way nutrient pollution (e.g., excess nitrogen or phosphorus) alters aquatic ecosystems and the likely ecological consequence.
Nutrient pollution causes algal blooms → hypoxia when algae decompose → fish kills and loss of biodiversity (eutrophication).
Describe the difference between gross primary productivity (GPP) and net primary productivity (NPP).
GPP is the total rate of photosynthesis (total energy fixed); NPP = GPP − energy used in plant respiration (energy available as biomass to consumers).
Describe how matter (e.g., carbon) cycles through an ecosystem, naming at least three reservoirs or processes
Carbon cycles through atmosphere (CO2), biosphere (organisms), hydrosphere (dissolved CO2), geosphere (fossil fuels, sediments); processes: photosynthesis, respiration, decomposition, combustion. 5
Describe how competition between two species for the same limited resource can lead to resource partitioning; give a concrete example.
Resource partitioning: species reduce competition by using different resources or using them at different times/places. Example: warblers feeding in different tree canopy zones.
Explain how density-dependent and density-independent factors differently affect population size; give one example of each.
Density-dependent: effects increase with population density (e.g., disease, competition). Density-independent: effects not related to density (e.g., natural disasters, temperature extremes).
Explain how climate change can shift species distributions and give one example of an ecological effect of such shifts.
Climate change shifts temperature and precipitation patterns, causing species to move poleward or to higher elevations; can disrupt species interactions (e.g., phenological mismatches between pollinators and plants).
Given a simple four-level food chain (grass → grasshopper → frog → snake), explain quantitatively why top predators are less abundant. Include a statement about energy availability and its effect on population size.
Each trophic transfer is inefficient (≈10% rule). If producers capture 10,000 J, herbivores get ~1,000 J, primary carnivores ~100 J, secondary carnivores ~10 J; less available energy supports fewer individuals at higher levels.
Compare and contrast a climax community with a successional stage in secondary succession, including causes and typical changes in species composition.
Climax community: relatively stable, mature community with established species composition. Successional stage: earlier, changing community after disturbance; secondary succession begins where soil remains and species composition shifts over time (pioneer → intermediate → late-successional species).
Define an invasive species and explain two ecological consequences invasive species can have on native communities.
Invasive species: nonnative species that negatively impact ecosystems (e.g., zebra mussels). Consequences: outcompete natives, alter food webs, reduce biodiversity, change nutrient cycling.
A population of rabbits grows rapidly after a predator population declines. Describe how delayed density-dependent factors could lead to population oscillations (cycles) between rabbits and predators.
When prey increase, predator populations rise later (time lag). Overconsumption can reduce prey below carrying capacity; predator numbers then fall; cycles continue as prey recover, producing oscillations.
Propose a management strategy to restore a degraded ecosystem (pick one strategy) and explain how it would improve energy flow, species interactions, or population stability. Include at least two expected ecological outcomes.
Example strategy: reforestation combined with invasive species removal and controlled reintroduction of native species. Expected outcomes: restored primary productivity and habitat connectivity, improved food-web stability, increased native population sizes and genetic exchange.