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Define population, community, ecosystem, and biome.
Answer: Population: one species in an area. Community: all species in an area. Ecosystem: community plus the abiotic environment. Biome: large region with a characteristic climate and community.
Levels of ecological organization.
What are the main symbiotic relationships?
Answer: Mutualism (both benefit), commensalism (one benefits, other unaffected), parasitism (one benefits, other harmed).
Clownfish and anemone; barnacles on whales; tapeworms.
What is the difference between r-selected and K-selected species?
Answer: r-selected: many offspring, little care, short lives (insects). K-selected: few offspring, high parental care, long lives (elephants).
Most species fall between.
Density-dependent vs density-independent limiting factors?
Answer: Density-dependent: competition, predation, disease (stronger as population grows). Density-independent: weather, natural disasters.
Both regulate population size.
Exponential vs logistic growth?
Answer: Exponential: unlimited growth (J-curve). Logistic: growth slows as it approaches carrying capacity (S-curve).
Carrying capacity (K) is the maximum sustainable population.
What is a niche?
Answer: The role of a species in its ecosystem: what it eats, where it lives, when it is active.
Competitive exclusion: two species cannot occupy the same niche indefinitely.
Primary vs secondary succession?
Answer: Primary starts on bare rock with no soil (after lava flow); secondary occurs where soil remains (after fire).
Pioneer species such as lichens begin primary succession.
What are the main threats to biodiversity?
Answer: Habitat destruction, invasive species, pollution, overexploitation, and climate change.
HIPPO mnemonic: habitat loss, invasive species, pollution, population, overharvesting.
What is eutrophication?
Answer: Nutrient runoff causes algae blooms that die and decompose, depleting oxygen and killing fish.
Caused by fertilizer and sewage.
What is biomagnification?
Answer: Toxins become more concentrated at higher trophic levels.
DDT in eagles.
Outline the nitrogen cycle.
Answer: Nitrogen fixation (bacteria convert N2 to ammonia), nitrification (to nitrites and nitrates), assimilation by plants, decomposition, and denitrification back to N2.
Legumes host nitrogen-fixing bacteria.
Outline the carbon cycle.
Answer: Photosynthesis removes CO2 from the air; respiration, decomposition, and combustion return it; carbon is stored in oceans, fossil fuels, and rock.
Burning fossil fuels raises atmospheric CO2.
What is a keystone species?
Answer: A species whose removal drastically changes the ecosystem, out of proportion to its abundance.
Sea otters control sea urchins, protecting kelp forests.
Producers, consumers, decomposers?
Answer: Producers make their own food (photosynthesis); consumers eat other organisms; decomposers break down dead matter and recycle nutrients.
Fungi and bacteria are key decomposers.
How much energy transfers between trophic levels?
Answer: About 10%; the rest is lost as heat and waste.
Why food chains rarely exceed four or five levels.
What is natural selection?
Answer: Individuals with heritable traits better suited to the environment survive and reproduce more, making those traits more common.
Darwin's mechanism of evolution.
What is sexual selection?
Answer: Selection for traits that improve mating success, even if they reduce survival.
Peacock tails.
Directional, stabilizing, and disruptive selection?
Answer: Directional favors one extreme; stabilizing favors the middle; disruptive favors both extremes.
Birth weight shows stabilizing selection.
What are the Hardy-Weinberg conditions?
Answer: No mutation, random mating, no gene flow, very large population, no selection.
p² + 2pq + q² = 1 and p + q = 1 when in equilibrium.
What is gene flow?
Answer: The movement of alleles between populations through migration.
Tends to make populations more similar.
What is the bottleneck effect?
Answer: A sharp reduction in population size that randomly changes allele frequencies and reduces diversity.
Cheetahs show low genetic diversity from a past bottleneck.
What is genetic drift?
Answer: Random changes in allele frequencies, most significant in small populations.
Bottleneck and founder effects are examples.
What are the main sources of genetic variation?
Answer: Mutation, sexual reproduction (crossing over, independent assortment, random fertilization), and gene flow.
Mutation is the ultimate source of new alleles.
What is fitness in evolutionary terms?
Answer: An organism's reproductive success relative to others in the population.
Not strength or speed; it is about passing on genes.
What four conditions are required for natural selection?
Answer: Variation, heritability, overproduction of offspring, and differential survival and reproduction.
Without heritable variation there is nothing to select.
What evidence supports evolution?
Answer: Fossils, comparative anatomy, embryology, molecular (DNA) comparisons, and biogeography.
More similar DNA suggests a more recent common ancestor.
Homologous vs analogous structures?
Answer: Homologous share a common ancestor (human arm, whale flipper); analogous share function but not ancestry (bird and insect wings).
Vestigial structures are reduced remnants (appendix).
What is convergent evolution?
Answer: Unrelated species evolve similar traits because of similar environments.
Wings in bats and birds; analogous structures.
Allopatric vs sympatric speciation?
Answer: Allopatric: populations separated geographically diverge. Sympatric: new species arise in the same area, often via polyploidy or niche differences.
Darwin's finches are a classic allopatric case.
What is a species (biological species concept)?
Answer: A group of organisms that can interbreed and produce fertile offspring.
Horses and donkeys produce sterile mules.
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