Category Archives: Ecosystems

Food webs and energy transfer

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Food_web

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Food chains illustrate the relationship between producers and consumers, showing the different trophic levels in an ecosystem. Because living organisms usually have more than one source of food, these food chains are often linked together, forming food webs. Food webs assist us to identify herbivores, carnivores, omnivores, scavengers, detritivores and decomposers in a community.

Not all relationships within an ecological community are predatory or feeding relationships. Some important relationships are parasitic, mutualistic (both organisms benefit), commensalism (one benefits, the other is not harmed) or parasitism (one benefits and the other is harmed, but usually not killed).

What is Ecological Succession?

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sand_dunes

What is ecological succession? This is the answer from Rolcam at the Ask Me Help Desk.

“Changes in communities occur over time in a process called ecological succession. This process occurs as a series of slow, generally orderly changes in the number and kinds of organisms that live in an area take place. Differences in the intensity of sunlight, protection from wind, and changes in the soil may alter the kinds of organisms that live in an area. These changes may also alter the number of populations that make up the community. Then, as the number and kinds of species change, the physical and chemical characteristics of the area undergo further changes. The area may reach a relatively stable condition called the climax community, which may last hundreds or even thousands of years. ”

The first plants that germinate in an area are called ‘pioneers’ and are usually grasses or ground covers. Weeds are effective pioneers on roadside verges for example, where they colonise bare round and provide shelter for other plants to grow.

“Ecologists distinguish two types of succession–primary and secondary. In primary succession, organisms begin to inhabit an area that had no life, such as a new island formed by a volcanic eruption. Secondary succession takes place after an existing community suffers a major disruption–for example, after a climax forest community is destroyed by fire. In this example, a meadow community of wild flowers and grasses will grow first, followed by a community of shrubs. Finally trees will reappear, and the area will eventually become a forest again. Thus, the forces of nature ultimately cause even climax communities to change.”

Do the following situations demonstrate primary or secondary succession?

  • Growth of grass trees after an intense bushfire in the Grampians National Park
  • Pisonia sp. forest that grows on a coral cay, Heron Island on the Great Barrier Reef
  • Open Acacia and Eucalyptus woodland that grows after volcanic action at Mt Eccles National Park
  • Sand dune vegetation that grows at Griffith’s Island, Port Fairy
  • Fern forest growing after glacier action in New Zealand

Population Ecology

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predator_prey_graph

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Population Ecology is the study of the numbers and distribution of groups of organisms. The Biology Q and A site has some good revision for exams at Population Ecology in question and answer format. Breathing Earth is the site I showed you in class with informative, animated graphics that show a comparison of births, deaths and CO2 emissions across the globe. It clearly shows how the rate of births and deaths in China, India and Africa differs to those in Australia and North and South America.

This Predator Prey simulation is based on a cardboard grid and game pieces representing rabbits and lynx. It demonstrates how the population of predator and prey impact on each other. At the Gould League site there is another activity that clearly shows how predator/prey populations interact with each other, this time with kangaroos and dingoes in an Australian ecosystem. Draw a graph of the data, showing the predator and prey in different colours. Then answer the following questions:

  1. What patterns can be seen in the graph? Suggest reasons for any patterns.
  2. Is there any relationship between the kangaroo and the dingo numbers? If so, account for this.
  3. The park management have decided to stop a rabbit prevention program because it is too expensive. What effect could this have on the dingo population and why?
  4. Identify the reasons for the absence of large migratory populations in Australia.

Biogeochemical Cycles

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Nitrogen_Cycle

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Chapter 14 is about the biogeochemical cycles that allow inorganic chemicals and carbon to be cycled through living organisms and non-living parts of ecosystems. There are four main cycles we need to consider and each group of students will prepare a presentation and poster about one of these systems:

Water – Chris and Catherine

Carbon – Charlotte and Tara

Nitrogen – Emily, Chloe and Stephanie

Phosphoros – James and Melissa

Australian Ecosystems

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ecosystem

Ecosystems – Geography for Kids Chapter 9: The Biosphere has great information about biogeochemical cycles (carbon, nitrogen, phosphoros etc), food chains and biomes.

Australia’s eight major ecosystem types are described at Gulliver Productions’ site.

Library ThinkQuest has information about the ten major biomes and how humans have affected ecosystems.

Windows to the Universe is an award-winning site with information about biomes and ecosystems.

Populations, Communities and Ecosystems

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map_of_human_impact

Image courtesy of the Center for International Earth Science Information Network Last of the Wild Project. This image shows the human footprint of different biomes across the earth, measured on an arbitary scale of 0 (minimum) to 100 (maximum) of human impact on each terrestrial biome.  Although increased human population often leads to sharper species and ecosystem declines, the researchers found that land transformation probably poses the single greatest threat to biodiversity, resulting in habitat loss and/or fragmentation. The authors also found that increased human access through roads, rivers, and coastlines can lead to more pollution and invasive species. Both human access and land transformation have been fueled by increased access to fossil fuel and electrical power.

This week we start Unit 2: Area of Study B: Dynamic Ecosystems. You will need to understand the following terms:

  • biotic (living) and abiotic (non-living)  factors
  • population (group of organisms of the same species)
  • community (the different species that live in  the same area)
  • ecosystem (the physical environment and living organisms that live within it)
  • producers (autotrophs – usually use the sun’s energy and inorganic materials to produce energy)
  • consumers (heterotrophs – need an organis source of energy)
  • herbivores (eat producer organisms)
  • carnivores (eat consumers)
  • omnivores (eat producers and consumers)
  • detritovores (eat detritus – that falls to the bottom of an ecosystem)
  • food chain (single chain of feeding relationships)
  • food web (interlinking chains of feeding relationships)

Try these great interactive food webs from the Gould League.