Ecology and Ecosystems: Energy Flow, Nutrient Cycling, Populations, Biodiversity and Maltese Habitats
Domain 2 tests how energy and matter move through ecosystems, how populations are estimated and regulated, and whether you can describe Maltese habitats with the right terms. Expect table interpretation (biomass, capture-recapture) and questions asking why a habitat is protected rather than just that it is.
Energy flow and nutrient cycling
- GPP is total fixation by producers; NPP = GPP − producer respiration, and only NPP is available to herbivores.
- About 10% of energy transfers between trophic levels; the rest is lost as heat in respiration, or passes to decomposers.
- Energy flows one way and is lost; nutrients cycle and are returned by detritivores and decomposers.
- Biomass pyramids can invert (phytoplankton vs zooplankton in open sea); energy pyramids never do.
Populations
- Exponential growth with unlimited resources; logistic growth approaches carrying capacity K through density-dependent limits (food, disease, space).
- r-strategists: many small offspring, fast, pioneer species. K-strategists: few, large offspring, parental care.
- Biodiversity has three levels: genetic, species, ecosystem/habitat.
Maltese habitats
- Maquis: tall, dense evergreen shrubs (lentisk, carob, mastic) that shade out competitors.
- Garrigue: low, open, aromatic scrub (thyme, spurge, esparto) on rocky karst, maintained by drought, grazing and fire.
- Steppe: annual grasses on abandoned or overgrazed fields.
- Valley systems (wied): seasonal watercourses; saline marshes at Għadira and Simar back sand-dune systems.
- Posidonia oceanica meadows: seagrass, not algae; clear-water indicator, nursery habitat, protected.
Worked example
Lincoln–Petersen estimate. 40 lizards are caught, marked, released; the second sample of 50 contains 8 marked individuals. N = (M × C) ÷ R = (40 × 50) ÷ 8 = 250. Assumptions that must be stated: closed population, no mark loss, marked animals mix and are equally catchable. A large proportion of marked animals in the second sample means the true population is small.
Traps that cost marks
- Reading the 10% rule as "energy falls by 10%" - it falls by about 90%.
- Calling Buskett ancient natural forest: it is largely planted (Aleppo pine, carob).
- Confusing NPP with GPP, or a capture-recapture estimate with a direct count.