Communities, Competition & Adaptations

Levels of organisation

• Individual: one organism. Population: all the organisms of one species in a habitat. Community: the populations of all the different species in a habitat. Ecosystem: the interaction of a community of living organisms (biotic) with the non-living (abiotic) parts of their environment
• To survive and reproduce, organisms need a supply of materials from their surroundings and from other organisms

Competition

• Plants compete for light, space, water and mineral ions from the soil
• Animals compete for food, mates and territory
• To suggest what organisms compete for in a habitat, look at what is in short supply there

Interdependence

• Within a community each species depends on others for food, shelter, pollination and seed dispersal. This is interdependence
• If one species is removed it can affect the whole community: its predators lose food, its prey increase, plants it pollinated fail to set seed
• A stable community is one where all the species and environmental factors are in balance, so population sizes stay fairly constant

Abiotic and biotic factors

• Explaining a change: identify the factor, say which organisms it affects directly, then follow the effect through the food chain. Less light means less photosynthesis, fewer plants, less food for herbivores, fewer predators

Adaptations

• Adaptations are features that let organisms survive in the conditions where they normally live:
  • Structural: body features. Thick fur, a layer of fat, small ears in the Arctic (less surface area to lose heat); large ears and thin bodies in deserts; spines and deep roots on cacti
  • Behavioural: what the organism does. Migration, hunting at night, huddling
  • Functional: how the body works. Hibernation, producing concentrated urine, camels tolerating large changes in body temperature
• Extremophiles live in extreme environments: very high temperature, pressure or salt concentration. Bacteria in deep sea vents are extremophiles