Ecology is the study of interactions among organisms and between organisms and their surroundings. (p.170)
Habitat is the natural living place of an organism. (p.170)
A species is a group of similar organisms able to interbreed and produce offspring. (p.171)
A population is a group of organisms of the same species living in the same habitat. (p.171)
A community is all populations of different species living in the same habitat and interacting. (p.171)
An ecosystem is communities living together in a habitat, interacting with each other and with abiotic components. (p.171)
A niche is the role of an organism in an ecosystem, including its behaviour and interactions with biotic and abiotic components. (p.171)
Biotic components are all living organisms; abiotic components are non-living elements such as water, air, soil, pH, temperature and light. (p.172)
Soil pH influences the distribution of organisms; most organisms live best at neutral or near-neutral pH. (p.172)
Most organisms live between 20 and 40 degrees Celsius; some survive extreme temperatures such as polar bears in tundra and foxes in deserts. (p.173)
Light intensity affects plant distribution: tall tropical rainforest trees form a canopy, so only small plants such as ferns grow below. (p.173)
Topography includes altitude, gradient and aspect, and determines humidity, temperature and light intensity. (p.174)
Higher altitude means lower relative humidity, atmospheric pressure and oxygen content. (p.174)
Microclimate is the climate of a small area that differs from its surroundings, e.g. under rocks or beneath forest canopies. (p.174)
Higher air humidity supports more organisms; low humidity increases transpiration and water absorption from soil. (p.175)
9.1.3 Nutrition and Trophic Levels
Autotrophs make their own food: photoautotrophs use light and carbon dioxide; chemoautotrophs use chemical energy from inorganic substances. (p.176)
Heterotrophs obtain food from other organisms: saprotrophs feed on dead matter, holozoic organisms ingest food, and parasites absorb nutrients from hosts. (p.176)
Biotic components are producers, consumers (primary, secondary, tertiary) and decomposers. (p.177)
Producers are autotrophs that make glucose from water and carbon dioxide using sunlight. (p.177)
Decomposers break down waste and dead organisms into simpler substances such as carbon dioxide and ammonia. (p.177)
A food chain shows energy transfer from producers to consumers and starts with a producer. (p.178)
A food web is a set of interconnected food chains showing feeding relationships in a community. (p.178)
9.1.6 Ecological Pyramids
A pyramid of numbers shows the number of organisms at each trophic level; numbers decrease up the pyramid while organism size increases. (p.180)
A pyramid of biomass shows total dry mass per unit area at each trophic level and decreases up the pyramid. (p.180)
A pyramid of energy shows that only about 10% of energy is transferred to the next trophic level; about 90% is lost as heat, living processes and excretion. (p.181)
9.1.7 Interactions among Biotic Components
The main interactions are saprophytism, symbiosis, predation and competition. (p.182)
Mutualism benefits both organisms, e.g. mynas eat lice from buffaloes. (p.182)
Commensalism benefits one organism without harming the other, e.g. remora fish eat scraps from sharks. (p.182)
Saprophytism: an organism obtains food from dead organic material, e.g. mushrooms on dead trunks. (p.182)
Predation: a predator eats its prey, e.g. an owl eats rats. (p.183)
Parasitism benefits one organism and harms the other, e.g. a tapeworm in the human intestine. (p.183)
Competition occurs when organisms compete for food, water, light and mates; intraspecific competition is within a species, interspecific competition is between species. (p.183)
9.1.8 Mangrove Ecosystem
Mangrove trees grow in estuaries where the sea meets the river. (p.185)
Abiotic conditions in mangroves include tidal waves and water, soft silty soil lacking aeration, strong wind, high light intensity, and high soil salt with low dissolved oxygen. (p.185)
Mangrove leaves have thick cuticles and sunken stomata, store water, and excrete excess salt through hydathodes. (p.187)
Pneumatophore roots project from the soil for aeration, e.g. Avicennia sp.; prop roots support the tree against wind and waves, e.g. Rhizophora sp.; buttress roots widen the base on soft soil, e.g. Bruguiera sp. (p.187)
Viviparous seeds germinate on the parent tree, so seedlings stick into mud and are not uprooted by waves. (p.187)
Colonisation is when plants conquer an uninhabited area and form colonies; succession is when dominant species are gradually replaced by successor species. (p.188)
In mangrove succession, pioneer species Avicennia sp. and Sonneratia sp. colonise the coastal zone, followed by Rhizophora sp. and then Bruguiera sp. inland. (p.188)
Mangroves act as natural barriers against waves and wind, provide protected sites for fish and shrimp, support migratory birds, and provide timber, charcoal, food and medicine. (p.189)
9.2 Population Ecology
Population ecology studies interactions between a population and its surroundings. (p.190)
Population distribution is affected by temperature, water, light, pH, mineral salt content, breeding sites and food supply. (p.190)
Population size is the number of organisms in a population; population density is the number of individuals per unit area. (p.191)
Patterns of distribution are clumped (uneven resources), random (little interaction) and uniform (competition for limited resources). (p.191)
A quadrat is a square frame used to estimate the population of slow-moving plants or animals by random sampling. (p.192)
Frequency = number of quadrats containing the species / total number of quadrats x 100%. (p.193)
Density = total number of individuals / (total number of quadrats x area of one quadrat). (p.193)
Coverage percentage = area covered by species / (total number of quadrats x area of one quadrat) x 100%. (p.193)
Capture-mark-release-recapture estimates the population of mobile animals: capture, mark, release, recapture, and count marked animals. (p.194)
Population size = (P x Q) / R, where P is the number in the first capture, Q the number in the second capture and R the number of marked animals in the second capture. (p.195)