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Flashcards · AP® Biology · Unit 8

Unit 8: Ecology flashcards

48 cards on topics 8.1 to 8.7. Pick a topic or study the whole unit.

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8.1 Responses to the Environment

How do behavioural and physiological responses differ?
Behavioural responses are actions such as moving, calling or hiding. Physiological responses are internal changes such as heart rate, flowering or making defensive chemicals.
What is the difference between taxis and kinesis?
Taxis: movement directed toward (+) or away from (−) a stimulus. Kinesis: speed or turning rate changes with stimulus strength, with no consistent direction. An end-point count alone cannot show taxis without path data.
How do innate and learned behaviours differ?
Innate behaviour is inherited and correct the first time. Learned behaviour changes with experience (imprinting, song learning, habituation). Selection favours both when they raise fitness.
How do organisms communicate, and why?
Through visual, audible, tactile, electrical and chemical signals, to warn, show dominance, find food, hold territory and attract mates. Link the signal to its fitness consequence, not to "the good of the species".
Why can a risky alarm call be favoured by selection?
If listeners are relatives, the caller's shared alleles survive in them: kin selection.
How do you test an animal choice-chamber result?
Chi-square against "no preference", df = categories − 1. 33 versus 17 of 50 (expected 25 each): χ² = 2.56 + 2.56 = 5.12 > 3.84, so reject the null hypothesis. Each animal is one independent count.
What makes a good control in a behaviour experiment?
It differs from the experiment only in the factor tested, for example both halves of a chamber dark to check for side bias.

8.2 Energy Flow Through Ecosystems

How do endotherms and ectotherms differ?
Endotherms heat themselves with metabolic heat and need much more food. Ectotherms follow the surroundings but regulate by behaviour (basking, shade, clustering). A mouse needs more food than a lizard of the same mass.
How do autotrophs get energy?
Photosynthetic autotrophs use light; chemosynthetic autotrophs use small inorganic molecules such as hydrogen sulfide, even without oxygen (for example at dark hydrothermal vents).
What is net primary productivity?
NPP = GPP − producer respiration: the energy available to consumers.
How much energy passes between trophic levels?
Usually about 10% (efficiency = next level ÷ this level × 100). From 8000 kJ in producers, about 8000 × 0.1 × 0.1 = 80 kJ reaches secondary consumers. Energy flows; it is not recycled.
What are the main steps of the nitrogen cycle?
Fixation (N₂ → NH₃ → NH₄⁺), assimilation, ammonification, nitrification (NH₄⁺ → NO₂⁻ → NO₃⁻) and denitrification (NO₃⁻ → N₂). The atmosphere is the largest reservoir, but plants cannot take N₂ from the air.
What are the main processes of the carbon cycle?
Photosynthesis removes CO₂; respiration, decomposition and combustion return it. Reservoirs: atmosphere, organisms, fossil fuels.
How does the phosphorus cycle differ from the carbon and nitrogen cycles?
It has no major gas phase. Weathering of rocks releases PO₄³⁻, producers take it up, it passes on by feeding and returns by excretion and decomposition.
How do you calculate an organism's energy budget?
Assimilated = ingested − egested; growth = assimilated − respired. Net gain leads to storage, growth and more offspring; net loss to mass loss and eventually death.

8.3 Population Ecology

What changes the size of a closed population?
Only births and deaths: dN/dt = B − D, where B and D are births and deaths per unit time in the whole population. It assumes no immigration or emigration.
What is the per capita growth rate?
r = (B − D) ÷ N, so dN/dt = rN. It lets you compare populations of different sizes. N = 500, B = 60, D = 35 per year: dN/dt = 25 per year, r = 0.05 per year.
What is exponential growth?
With no constraints on reproduction, the per capita rate stays at its maximum: dN/dt = rₘₐₓN. Per capita rate and doubling time stay the same while dN/dt and N keep increasing. It cannot last because resources run short.
How does exponential growth look on graphs?
A steeper and steeper J on a linear y-axis, and a straight line on a log y-axis, because equal steps on a log axis are equal ratios.
How should population data be graphed?
A line graph of N against time, time on the x-axis, labels and units on both axes, an even scale, means with error bars for replicates, and a log y-axis for exponential data. Not a bar chart.
What is a population?
All the individuals of one species in one area at one time. A group of several species is a community, not a population.

8.4 Effect of Density on Populations

What is carrying capacity?
K is the sustainable population size supported by the ecosystem's total available resources. It is set by the limiting resource and changes when the environment changes; it is not fixed for a species.
What is the logistic growth equation?
dN/dt = rₘₐₓN(K − N)/K. (K − N)/K is the unused share of K. rₘₐₓ = 0.5 per month, K = 400, N = 100: 0.5 × 100 × 300 ÷ 400 = 37.5 per month. Divide by K, not N.
At what population size is logistic growth fastest?
At N = K/2, where maximum dN/dt = rₘₐₓK/4. Near K growth slows to zero as births balance deaths (they do not stop); above K the population falls.
What are density-dependent factors?
Competition, predation, disease and parasites, waste build-up and territorial stress. Their effect per individual grows with density, so they can hold N near K.
What are density-independent factors?
Frost, storms, floods, drought and fire. They remove about the same fraction at any density, so they cannot hold N steady. Classify by the fraction killed, not the number.
Why do per capita births fall and deaths rise as density increases?
Each individual gets less food, water, light or space, so the population levels off in an S-shaped (logistic) curve.

8.5 Community Ecology

What do species richness, evenness and diversity mean?
Richness: how many species. Evenness: how equally individuals are shared among them. Diversity combines richness and evenness; judging by richness alone ignores evenness.
How do you calculate Simpson's diversity index?
Diversity index = 1 − Σ(n/N)². Two species with 5 each: 1 − (0.25 + 0.25) = 0.50. With 9 and 1: 1 − (0.81 + 0.01) = 0.18, same richness but less even.
What are the signs for each type of species interaction?
Competition −/−; predation and herbivory +/−; parasitism +/−; mutualism +/+ (pollination); commensalism +/0.
Why does the predator population peak after the prey peak?
Predators need time to turn extra food into extra offspring, so predator numbers lag behind prey numbers.
What are niche partitioning and competitive exclusion?
Similar species can coexist by dividing a resource in time, space or type (niche partitioning); without it, one may exclude the other (competitive exclusion).
What is a trophic cascade?
Effects passed down a food chain, alternating in direction (down, up, down) at each level.
How do you read ± 2 SE error bars when comparing sites?
SE = s ÷ √n. Non-overlapping bars: the means are probably different. Overlapping bars do not prove there is no difference.

8.6 Biodiversity

What is the difference between ecosystem resistance and resilience?
Resistance: how little an ecosystem changes when disturbed. Resilience: how fast and how fully it recovers.
Why are diverse ecosystems more resilient?
Diversity gives back-up species (functional redundancy), alternative food-web pathways and a variety of responses to stress. Systems with few, similar parts, such as a single-variety crop, are fragile. Diverse systems can still be damaged.
What is a keystone species?
A species with an effect disproportionate to its abundance, usually by controlling a dominant competitor or grazer: the ochre sea star on rocky shores, sea otters in kelp forests. It is not the most abundant species.
What happens when a keystone predator is removed?
Short term: its prey, often a dominant competitor, increases. Long term: that species spreads, many others are lost and the community simplifies.
What maintains an ecosystem's diversity?
Producers, keystone species and essential abiotic and biotic factors. Changing an essential abiotic factor such as water shifts composition to tolerant species.
How do you quantify resistance and recovery?
Percentage change = (new − original) ÷ original × 100 for the fall (300 to 240 g m⁻² is a 20% fall). Recovery = after ÷ before × 100 for resilience.

8.7 Disruptions in Ecosystems

What is heterozygote advantage?
The heterozygote has higher relative fitness than either homozygote, so both alleles persist, as with sickle-cell trait where falciparum malaria is common.
Why do invasive species spread?
They escape their predators and diseases, use an open niche, or outcompete natives (kudzu, zebra mussels). Not every introduced species is invasive.
What is biomagnification?
A persistent, fat-soluble toxin is kept as biomass passes up the food chain, so top predators are most contaminated. 0.02 ppm rising 10 times at each of three steps reaches 20 ppm.
How does eutrophication create a dead zone?
Nutrients cause an algal bloom; the algae die and aerobic decomposers break them down, using up O₂, causing low oxygen and fish deaths. Decomposers, not living algae, cause the oxygen crash.
How do human activities disrupt ecosystems?
Habitat loss (logging, urbanisation), monocropping (potato blight), introduced diseases (Dutch elm disease), climate change, biomagnification and eutrophication. Fast change can cause extinctions.
How do geological and meteorological events disrupt ecosystems?
El Niño (warm surface water, weak upwelling, fewer nutrients, so plankton, fish and seabirds decline), continental drift and the meteor impact about 66 million years ago change habitats and distributions.
What are the critical chi-square values at p = 0.05?
3.84 (1 df), 5.99 (2 df), 7.81 (3 df). Use counts, not percentages; df = categories − 1. Use "fail to reject" and "support", never "accept" or "prove".
Does an environmental change cause helpful mutations?
No. Mutations arise at random; a changed environment favours variants that already exist, shifting allele frequencies.

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