This free ecology practice test PDF covers every major topic tested on AP Environmental Science, college ecology exams, and environmental certification assessments. Download it, print it, and work through questions on population dynamics, community interactions, ecosystem energy flow, biogeochemical cycles, biomes, and biodiversity threats — all organized for efficient offline study.
The PDF is structured around the core content domains that appear on AP Environmental Science (APES), college-level ecology midterms and finals, and environmental certification exams. Each section below explains the key concepts and how they are tested.
Ecology is organized into a hierarchy: individual organism → population (all individuals of one species in an area) → community (all populations in an area) → ecosystem (community plus its abiotic environment) → biosphere (all ecosystems on Earth). Exam questions test your ability to identify which level of organization a scenario describes and to distinguish ecological concepts that apply at one level but not another.
Population growth models are a consistent exam focus. Exponential growth (J-curve) occurs when resources are unlimited — populations grow at a constant rate proportional to their size. Logistic growth (S-curve) occurs when resources are limited — growth slows as population approaches carrying capacity (K). The growth rate formula r = (b – d) + (i – e) is frequently tested, where b = birth rate, d = death rate, i = immigration, and e = emigration. R-selected species (high reproduction, low parental investment, short life span) and K-selected species (low reproduction, high parental investment, long life span near K) represent opposite ends of the life history spectrum.
Communities are structured by species interactions. Predator-prey dynamics follow cyclical patterns — predator populations lag behind prey peaks. The competitive exclusion principle states that two species competing for identical resources cannot coexist indefinitely; one will outcompete the other unless they differentiate their niches. The fundamental niche is the full range of conditions a species could theoretically occupy; the realized niche is the narrower range it actually occupies due to competition and predation. Keystone species have a disproportionately large effect on community structure relative to their biomass — their removal causes dramatic shifts in species composition. Succession describes directional community change: primary succession starts on bare substrate with no soil; secondary succession follows a disturbance that leaves soil intact.
Energy flows through ecosystems in one direction: from producers (autotrophs that fix solar energy through photosynthesis) through primary consumers (herbivores) to secondary consumers (carnivores that eat herbivores) and beyond. The 10% energy transfer rule states that only approximately 10% of the energy stored at one trophic level is available to the next — the rest is lost as heat through cellular respiration. Trophic pyramids can represent energy, biomass, or numbers; energy pyramids always have a narrow top because so much is lost at each transfer.
Biogeochemical cycles describe how matter moves between living organisms and the abiotic environment. Unlike energy (which flows through and is lost from ecosystems), matter cycles continuously. The nitrogen cycle is among the most tested: nitrogen gas (N2) is fixed into usable forms by nitrogen-fixing bacteria (both free-living and symbiotic in root nodules of legumes). Nitrification converts ammonium to nitrite then nitrate. Plants assimilate nitrate. Decomposers return nitrogen to ammonium through ammonification. Denitrifying bacteria return nitrogen gas to the atmosphere.
The carbon cycle links photosynthesis, cellular respiration, decomposition, and combustion. Photosynthesis pulls CO2 from the atmosphere into organic molecules. Respiration by all organisms releases CO2 back. Decomposition of dead organic matter releases CO2 and methane. Human combustion of fossil fuels (ancient stored carbon) has accelerated the cycle, increasing atmospheric CO2 concentrations and driving climate change.
Biomes are large-scale terrestrial ecosystems defined by climate — primarily temperature and precipitation. The tropical rainforest has the highest biodiversity and productivity, with warm temperatures and high rainfall year-round. Temperate deciduous forests have seasonal variation and moderate productivity. Grasslands receive too little rainfall for forests but too much for deserts and support large grazing animal populations. Deserts receive less than 250mm of precipitation annually and have extreme temperature swings. The tundra is the coldest biome, with permafrost, low productivity, and low biodiversity — but it stores enormous amounts of carbon in frozen soil.