B16 - Adaptations, interdependence, and competition

• Community


  Made up of the populations of different species of animals and plants, protista, fungi, bacteria, and archaea that are all interdependent in a habitat
• Ecosystem


  Made up of a community of organisms interacting with the non-living or abiotic elements of their environment
• Interactions between animals and plants in an ecosystem

  • Plants produce food by photosynthesis
  • Animals eat plants
  • Animals pollinate plants
  • Animals eat other animals
  • Animals use plant and animal materials to build nests and shelters
  • Plants need the nutrients from animal droppings and decay
• Stable community


  • Environmental factors are relatively constant, species of living organisms may also be in balance, number of species remains relatively constant, population sizes of the different species remain relatively constant
  • Examples: tropical rainforests, ancient oak woodlands, mature coral reefs
• Within a stable community, change can be tolerated and absorbed, but when a large, stable community is lost, it cannot easily be replaced
• Abiotic factors that affect communities include light intensity, temperature, moisture levels, soil pH and mineral content, wind intensity and direction, availability of oxygen, and availability of carbon dioxide
• Carnivorous plants


  Thrive where nitrate levels are very low because they can trap and digest animal prey, providing the nitrates they need
• Low (acidic) soil pH


  Inhibits decay
• Strong prevailing winds


  Affect the shape of trees and the whole landscape, and cause plants to transpire fast
• Abiotic factors that affect communities do not work in isolation, they interact to create unique environments
• Biotic factors affecting communities

  • Availability of food
  • New pathogens or parasites
  • New predators arriving
  • Interspecific competition (competition between species)
• Animals, plants, fungi, protista, bacteria, and archaea are all involved in constant struggles between members of the same species and between members of different species in their community for its resources
• Ecologists study the make-up of biological communities and ecosystems, looking at how living and non-living factors affect the abundance and distribution of organisms
• Quadrat


  A square frame laid on the ground to outline a sample area, used to investigate the size of a population of plants or slowly moving animals
• Quadrats with sides 0.5 m long give a 0.25 m² sample area
• Quadrat


  A square frame laid on the ground to outline a sample area
• Ecologists study the make-up of biological communities and ecosystems
• Ecologists look at how living and non-living factors affect the abundance and distribution of organisms
• Ecologists investigate the effect of changes in the environment on the organisms in a particular ecosystem
• To study ecosystems, ecologists must be able to measure how many organisms there are and how those organisms are distributed
• Quadrats


  • The simplest way to count the number of organisms is to use a sample area called a quadrat
  • Quadrats are often square frames laid on the ground to outline the sample area
• Quadrat size


  A quadrat with sides 0.5 m long gives you a 0.25 m² sample area
• Quadrats are used to investigate the size of a population of plants and can also be used for slowly moving animals like snails or sea anemones
• Using quadrats


  1. Use the same size quadrat every time

  2. Sample as many areas as possible

  3. Choose sample areas at random
• Random sampling


  Ensures results reflect the true distribution of organisms and conclusions will be valid
• Ensuring random sampling


  1. Person with quadrat closes eyes, spins, opens eyes, walks 10 paces, drops quadrat

  2. Use a random number generator to decide where to drop quadrat
• Quantitative sampling


  Taking several random quadrat readings and finding the mean number of organisms per m²
• Quantitative sampling can be used to compare distribution of the same organism in different habitats or compare variety of organisms in different habitats
• Finding statistics from quadrat data

  1. Range (min to max values)

  2. Mean (sum of values divided by number of values)

  3. Median (middle value when ordered)

  4. Mode (most frequently occurring value)
• Sampling along a transect is another way to measure distribution of organisms
• Transect


  A line stretched between two points, often where a change is linked to an abiotic factor, along which organisms are sampled at regular intervals
• Transects show how the distribution of organisms changes along a line, and physical factors like light and soil pH can also be measured
• Measuring population size and distribution


  1. Choose a common species to study

  2. Decide on an abiotic or biotic factor to investigate

  3. Measure population throughout habitat

  4. Take transect with regular quadrats to investigate changes
• Safety: Follow health and safety instructions
• Plants


  • They compete for light for photosynthesis, to make food
  • They compete for water for photosynthesis and for keeping their tissues rigid and supported
  • They compete for nutrients (minerals) from the soil, to make all the chemicals they need in their cells
  • They compete for space to grow, allowing their roots to take in water and nutrients and their leaves to capture light
• Plants are in competition both with other species of plants and with their own species
• Big, tall plants such as trees take up a lot of water and nutrients from the soil and reduce the amount of light reaching the plants beneath them
• When a plant sheds its seeds they might land nearby. In this case, the parent plant will be in direct competition with its own seedlings
• The roots of some desert plants even produce a chemical that stops seeds from germinating, killing the competition before it even begins to grow
• Plants that grow close to other species

  • They often have adaptations to help them avoid competition
  • Small plants found in woodlands often grow and flower very early in the year
  • Some plants have different types of roots - shallow roots taking water and nutrients from near the surface, and long, deep roots going far underground
  • If one plant is growing in the shade of another, it may grow taller to reach the light or grow leaves with a bigger surface area