B16 Adaptations, interdependence, and competition


B16.1 Importance of communities

Populations include organisms of the same species. Populations live in communities, which are made up of many populations, which are all interdependent in a habitat. Interdependent means to be dependent on other species for food, shelter, seed dispersal, etc.

An ecosystem involves communities of organisms interacting with abiotic factors. Biotic elements are the interactions of organisms. 

The Sun is the source of the energy transferred through ecosystems within chemical bonds of organisms. Materials like carbon, nitrogen, and water are constantly recycled in processes including microorganisms.

Examples of interdependence include plants producing food by photosynthesis and the animals eating the plants. Animals eat other animals, and use plant and animal materials to build nests or shelters. Plants need nutrients from animal droppings and decay. 

Different animals and plants compete for various resources within each species and other species. If one population becomes very numerous, or remoed, it can affect the whole community.

A stable community involves relatively constant environmental factors, but if they do change, it is in a regular pattern, like a seasonal pattern. As a result the number of species remains constant, as does the sizes of populations of different species. When a large, stable community is lost, it is not easily replaced.

B16.2 Organisms in their environment

To survive and breed successfully, organisms must be well-adapted.

Abiotic factors affect organisms and their communities.:

  • Light intensity can limit photosynthesis, and affect the distribution of plants and animals. Plants adapted to lower light levels have bigger leaves or more chlorophyll. The breeding cycles of many organisms are linked to light intensity and length of the day
  • Temperature could also limit photosynthesis, and the growth of plants. Low Arctic temperatures mean that plants are small, affecting the number of herbivores and carnivores in the community
  • Moisture levels: If there is no water, there is limited life. There is limited life in deserts due to the limited availability of water. When it rains, many plants flower, grow, and make seeds quickly when water is available. These plants are eaten by many animals moving into the area
  • Soil pH and mineral content: The level of mineral ions affects the distribution of plants. Plants like sundews thrive where nitrate levels are low, so they can digest and trap prey, and they get nitrates they need from the animal protein. Soil pH affects rate of decay and release of mineral ions. If it is acidic, it inhibits decay
  • Wind intensity and direction: In areas with strong prevailing wind, plant shape and landscape is affected. Transpiration occurs faster
  • Availability of oxygen affects aquatic organisms. Some invertebrates can survive in waters with very low oxygen levels but most fish need a high level of dissolved oxygen. Proportion of oxygen in the air varies little
  • Carbon dioxide levels impact photosynthesis and plant growth, and the distribution of organisms. Mosquitos are attracted to high carbon dioxide levels

Biotic factors include the availability of food - if there's lots of food, organisms can breed successfully; a


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