Lesson 13 of 13 · 13 min
Chapter review
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Must-know facts
20 facts
- 01Ecology works at four levels: organisms, populations, communities, biomes.
- 02Natural selection acts at the population level, which links population ecology to genetics and evolution.
- 03Population attributes: birth rate, death rate, sex ratio, age distribution; rates are per capita.
- 04Lotus: 8 new on 20, birth rate 0.4 per lotus per year. Fruit flies: 4 of 40 die, death rate 0.1 per fly per week.
- 05Age pyramid shapes show growing, stable or declining populations.
- 06Population density N can be a number, per cent cover or biomass; relative density (fish per trap) often suffices.
- 07Tiger census uses pug marks and fecal pellets.
- 08Nt+1 = Nt + [(B + I) − (D + E)]; natality and immigration add, mortality and emigration subtract.
- 09Exponential: dN/dt = rN, r = b − d; Nt = N0 e^(rt); J-shaped curve.
- 10r values: Norway rat 0.015, flour beetle 0.12, India (1981) 0.0205.
- 11Logistic: dN/dt = rN (K − N)/K; sigmoid curve with lag, acceleration, deceleration, asymptote at K.
- 12Logistic growth (Verhulst-Pearl) is the more realistic model.
- 13Breed once: Pacific salmon, bamboo. Many small offspring: oysters, pelagic fishes.
- 14Signs: mutualism +/+, competition −/−, predation and parasitism +/−, commensalism +/0, amensalism −/0.
- 15Prickly pear in Australia controlled by a cactus-feeding moth; Pisaster removal led to over 10 invertebrate species going extinct.
- 16Nearly 25 per cent of insects are phytophagous; Calotropis makes cardiac glycosides.
- 17Gause: Competitive Exclusion Principle; MacArthur: five warbler species co-exist by resource partitioning.
- 18Connell: Balanus excludes Chthamalus on the Scottish coast (competitive release when removed).
- 19Human liver fluke needs a snail and a fish; the koel lays eggs in the crow's nest (brood parasitism).
- 20Commensalism: orchid on mango, barnacles on whale, cattle egret, clown fish; mutualism: lichen, mycorrhiza, fig-wasp, Ophrys.
Common traps
Where marks are lost
Key terms
18 terms
- Population
- Individuals of one species in a defined area that share or compete for resources and can interbreed.
- Birth rate
- Births per member of the population in a given period.
- Sex ratio
- The proportion of females and males in a population.
- Age pyramid
- A plot of the per cent of individuals in each age group, showing growth status.
- Population density (N)
- Population size, measured as numbers, per cent cover or biomass.
- Natality
- Number of births added to a population in a given period.
- Emigration
- Individuals leaving the habitat for elsewhere in a given period.
- Intrinsic rate of natural increase (r)
- r = b − d, per capita birth rate minus per capita death rate.
- Carrying capacity (K)
- The maximum population a habitat can support for a species.
- Logistic growth
- Growth that slows as N approaches K, giving a sigmoid curve.
- Darwinian fitness
- Reproductive fitness, a high r value.
- Mutualism
- An interaction in which both species benefit.
- Commensalism
- One species benefits, the other is unaffected.
- Amensalism
- One species is harmed, the other is unaffected.
- Competitive release
- A species expands its range when a superior competitor is removed.
- Resource partitioning
- Competing species co-exist by using a resource at different times or in different ways.
- Brood parasitism
- A bird laying eggs in another species' nest for it to incubate, like the koel in a crow's nest.
- Co-evolution
- Linked evolution of two interacting species, such as a flower and its pollinator.