Unit 2: Dynamic Ecosytems

The environment refers to all the factors present that impact on an organism. We categorise an environment into the abiotic and biotic factors.

Abiotic factors are the physical and chemical factors present in an environment. Some examples are temperature, light intensity, pH of the soil, concentration of oxygen in water, etc.

Biotic factors refer to the living things within the environment. Some examples include the presence of organisms of the same species, competitors (compete for food, water, etc), collaborators (work with the species to an advantage), predators, parasites, etc.

Differences in physical conditions vertically across a habitat give rise to stratification.

Differences in abiotic conditions give rise to stratification. These differences include the amount of light present, the strength of the wind and the humidity.

These different conditions support different communities of organisms.

Just are varying abiotic factors in a rainforest lead to stratification, the changing water

level associated with tides creates intertidal zonation.

It is important to measure factors within environments to better understand how they function. This knowledge is vital to conservation and restoration of the natural environment.

Qualitative data refers to descriptions not involving numbers. E.g. the environment on the side of the cliff is rocky and very exposed to the elements.

Quantitative data involves measurements e.g. the average temperature during the day was 32 degrees.

Geographic range refers to the area over which can organism is found.

Geographic distribution refers to the spread of an organism within an ecosystem.

Abundance refers to the number of organisms present in an ecosystem

Geographic Range of the Platypus.

What limits range and distribution? The resources available in an environment and the ability of the organism to obtain these resources (dependent on adaptations) limit the organisms range and distribution. Generally the greater the tolerance range of an organism the greater its range and distribution. Biotic factors can be responsible for limiting distribution within an ecosystem. Such factors include food sources and predators.

It is important to know not only which species of organisms are present in an ecosystem and the relationships that exist between then but also where exactly these species are located within the ecosystem and how many of them are alive.

Species are rarely spread evenly through an ecosystem rather they occur in patterns of distribution. Some common patterns are:

Random distribution- organisms are irregularly spaced and the location of one species does not appear to affect the location of another; more common in plant populations.

Uniform or continuous distribution- organisms are evenly spaced the presence of one organism determines how close or distant another organism will be; common in animal populations that are territorial.

Clumped or grouped distribution- a number of individuals are grouped together and the groups make up the population as a whole; this may be to do with social behaviours such as schools of fish

It is not always possible to directly measure a population. How can you count all of the birds within an ecosystem or all of the blades of grass?

Instead ecologists use sampling techniques to provide estimates of populations.

Such techniques include transects, quadrats, and capture-mark-recapture.

For organisms that do not move a quadrat can be a good method of estimating distribution and abundance. Quadrats can also be used to measure density. The position of quadrats within an ecosystem is selected at random. The number of particular species within the quadrat are counted and recorded. The total of all of the quadrats are averaged.

A line transect can be used to measure the distribution of species in an ecosystem. They are especially helpful where we see environmental gradients- gradual changes in an ecosystem.

We can also use vertical transect to investigate stratification in forests for example where different amounts of light, humidity and wind levels impact different species.

Capture-mark-recapture is a method used to estimate the population of mobile species.

Step 1 is to capture organisms randomly in a way that they are not harmed.

Step 2 is to mark these organisms ensuring that the marking does not attract predators or cause harm. Tagging is a common form of marking animals. Insects are usually marked with a dot of ink. The animals are then returned to the environment.

Step 3 occurs some time after release. Organisms are captured again and the number of marked organisms is counted. From this information the population is estimated using the formula below:

Dr. T., an ecologist, wanted to find out how many frogs live in a small pond.

On the first trip to the pond, 55 frogs were caught, banded, and released.

The second trip to the pond, 72 frogs were caught, of those 72 frogs, 12 were banded.

Assuming the banded frogs had thoroughly mixed with the unbanded frogs, how many frogs live in the pond?

55 frogs were caught, banded

The second trip to the pond, 72 frogs were caught, 12 were banded

Remember:

= 330frogs

Information

Density refers to the number of individuals in a given area. Knowing the density of a population can help assess whether or not an ecosystem is able to provide sufficient resources to support populations. This is known as the carrying capacity of the ecosystem.