A student estimated the population size of marram grass clumps in a sand dune. A $0.25\ \text{m}^2$ quadrat was placed at five random coordinates in a $120\ \text{m}^2$ study area. The numbers of clumps in the quadrats were 3, 1, 4, 0 and 2.

A population of woodlice was estimated using capture-mark-release-recapture. In the first sample, 48 woodlice were captured, marked harmlessly and released. In the second sample, 60 woodlice were captured, of which 12 were marked.

Aphids feeding on bean plants reproduce rapidly when first introduced into a greenhouse. After several weeks, the aphid population fluctuates around a relatively stable size.

Duckweed was grown in nutrient solution in identical containers. The graph shows the number of duckweed fronds over time.

A shallow reef contains hard corals, zooxanthellae, grazing fish, predatory fish, fungi and bacteria. Abiotic factors include light intensity, temperature and salinity.

Black walnut trees release juglone into the soil. Penicillium fungi release penicillin-like compounds into their surroundings.

Ecologists estimated the population size of a sessile coastal plant, sea rocket (Cakile maritima), on a sand-dune area. A grid was marked over the habitat and ten random coordinates were selected. A quadrat of area $0.25\ \text{m}^2$ was placed at each coordinate.

A population of ground beetles in a woodland was estimated using capture-mark-release-recapture. Beetles were marked with a small harmless dot of paint and released at the capture site. A second capture was made three days later.

Hard corals contain photosynthetic algae called zooxanthellae in their cells. Researchers measured coral growth and the density of zooxanthellae under two temperature treatments.

Field observations show that seaweed species A is abundant on rocks where seaweed species B is absent, but species A is rare where species B is present.

Historical records from northern forests show repeated cycles in snowshoe hare and Canada lynx populations. Hare numbers usually increase before lynx numbers increase.

In a kelp forest, sea otters feed on sea urchins, and sea urchins graze kelp. In some years, nitrate availability in seawater is low.

In some New Zealand beech forests, introduced common wasps feed heavily on honeydew produced by scale insects. Honeydew is also used as food by endemic birds and insects.

Duckweed fronds were grown in identical trays of nutrient solution under controlled light and temperature. The number of fronds was counted every two days.

A deer population on an island was monitored for six years. Researchers recorded deer density, prevalence of a parasitic nematode and survival of fawns to one year old.

Four pond mesocosms were set up with equal volumes of pond water containing phytoplankton and zooplankton. Some mesocosms received extra phosphate and some received a fish predator that feeds on zooplankton. Phytoplankton biomass was measured after ten days.

Two investigations tested chemical interactions between organisms. In one, tomato seedlings were grown in soil containing different concentrations of juglone from black walnut. In the other, paper discs containing filtrate from Penicillium cultures were placed on agar seeded with bacteria.

Emperor penguin chicks form crèches while adults forage at sea. Researchers recorded chick survival and mean body mass change in groups of different sizes during a period of cold weather and limited food delivery.

Two barnacle species were surveyed at 30 randomly selected sites on a rocky shore. The observed counts were: both species present, 3 sites; species A only, 12 sites; species B only, 10 sites; neither species present, 5 sites. Expected frequencies for a chi-squared test of association are 6.5, 8.5, 6.5 and 8.5 respectively. The critical value of $\chi^2$ at $p = 0.05$ and $df = 1$ is 3.84.

In a New Zealand beech forest, introduced wasps feed on honeydew produced by scale insects. Honeydew is also used by endemic birds and insects. Researchers measured wasp density and the proportion of available honeydew removed during summer.

Historical trapping records have been used as an indirect measure of Canada lynx and snowshoe hare population sizes in northern forests. The graph shows relative abundance over several cycles.

The spread of an introduced bird population was monitored for eight years after colonization of a region. The same data were plotted on two graphs: one with a linear vertical axis and one with a logarithmic vertical axis.

A population of a sessile shore plant was surveyed in a rectangular salt marsh. Students used random coordinates to place quadrats and counted the number of plants in each quadrat.

A conservation team estimated the population size of a motile lizard in a dry woodland using capture-mark-release-recapture. Lizards were marked with a small non-toxic paint spot before release.

Meerkats live in groups in which individuals forage for insects, compete for breeding opportunities and sometimes produce alarm calls when predators approach.

Black walnut trees release juglone into the surrounding soil. Some fungi such as Penicillium release antibiotic compounds into soil where bacteria are growing.

Two barnacle species were recorded as present or absent in 100 randomly selected quadrats on a rocky shore. A chi-squared test was used to test for association between the species. The critical value at $p=0.05$ with $1$ degree of freedom is $3.84$.

A population of freshwater snails in a pond fluctuates around a long-term average. In summer, snail density increases rapidly, followed by a rise in a fungal disease and increased predation by ducks.

Duckweed fronds were grown in identical trays of nutrient solution. The number of fronds was recorded every two days to model population growth under controlled conditions.

The diagram shows three mutualistic relationships: legumes with nitrogen-fixing bacteria in root nodules, orchids with mycorrhizal fungi and hard corals with zooxanthellae.

Ecologists observed that a native grass species was more abundant in plots where an introduced grass species was absent. They proposed that the introduced grass reduces the native grass population by interspecific competition for soil nitrate.

Long-term records of snowshoe hare and Canada lynx numbers show repeated cycles in northern forests. Hare numbers generally increase before lynx numbers increase.

A coastal food chain includes sea otters, sea urchins and kelp. In some bays, sea otter numbers declined sharply. In other bays, nitrogen concentration in the water decreased after changes in ocean currents.

In a New Zealand beech forest, introduced common wasps and German wasps feed heavily on honeydew produced by scale insects. Honeydew is also an important food resource for endemic birds and insects.

Two sessile barnacle species were recorded as present or absent in randomly selected quadrats on a rocky shore. The data were analysed using a chi-squared test for association.