Ecosystems and Biodiversity - TCE Environmental Science (Tasmania)
“Describe the structure of ecosystems and explain why biodiversity at gene, species and ecosystem levels matters for ecological function.”
An ecosystem is a community of interacting organisms together with the non-living environment they live in. Biodiversity is the variety of life measured at three levels: genetic, species and ecosystem. Higher biodiversity generally makes ecosystems more productive, stable and resilient because different species perform different roles, so the loss of biodiversity weakens ecological function.
What this dot point is asking
This dot point asks you to describe how an ecosystem is put together, and to explain why the variety of life it holds, its biodiversity, is essential to keeping that ecosystem working. You should be able to define the levels at which biodiversity is measured and link them to ecological function using real Tasmanian and Australian examples.
The structure of an ecosystem
An ecosystem has two parts that constantly interact. The biotic component is every living thing, from bacteria and fungi to plants and animals. The abiotic component is the non-living environment: sunlight, temperature, water, soil, nutrients, salinity and pH. These parts are organised into a hierarchy. A single organism belongs to a population of its own species, populations of different species form a community, and the community together with its abiotic surroundings forms the ecosystem.
Each species occupies a niche, which is its particular role and position in the ecosystem, including what it eats, where it lives, when it is active and how it interacts with others. The habitat is the physical place a species lives, while the niche is the way it makes a living there. When two species compete for the same niche, one usually outcompetes the other, so coexisting species tend to divide resources.
Levels of biodiversity
Biodiversity is described at three connected levels.
- Genetic diversity is the variety of genes within a single species. A population with high genetic diversity has more variation to draw on when conditions change. The Tasmanian devil shows the danger of low genetic diversity, because its limited variation helped Devil Facial Tumour Disease spread so quickly.
- Species diversity is the number of different species in an area (richness) and how evenly individuals are spread among those species (evenness). A Tasmanian wet eucalypt forest has high species diversity.
- Ecosystem diversity is the variety of ecosystems within a region, such as the alpine moorlands, rainforests, buttongrass plains and giant kelp forests found across Tasmania.
A keystone species has a disproportionately large effect on its ecosystem relative to its abundance, so its removal causes major change. The sea otter is a classic global example; in Tasmanian giant kelp forests, sea urchin grazing pressure illustrates how losing predators reshapes an ecosystem.
Why biodiversity supports ecological function
High biodiversity supports the processes that keep ecosystems running. Different species capture energy, recycle nutrients, pollinate plants, control pests and build habitat. Because more than one species often performs a similar role, this functional redundancy means an ecosystem can keep working even if one species declines. This buffering effect makes biodiverse ecosystems more resilient to disturbances such as fire, drought or disease.
Biodiversity also supports productivity and stability. A varied community uses available resources such as light, water and nutrients more completely than a single species could, so total productivity tends to rise. Diverse food webs have many alternative pathways, so the loss of one link is less likely to collapse the whole system.
Tasmania's giant kelp (Macrocystis pyrifera) forests are a strong example. These underwater forests once fringed the east coast, providing habitat, food and shelter for fish, invertebrates and seals. Warming waters and the spread of the long-spined sea urchin have destroyed most of them, turning structured forests into bare urchin barrens with far lower biodiversity and far less ecological function. The collapse shows how the loss of one structuring species and rising temperatures can strip an ecosystem of the variety that kept it productive.
Always link biodiversity back to function. Genetic diversity lets species adapt, species diversity provides functional redundancy and resilience, and ecosystem diversity spreads risk across a landscape. Examiners reward answers that connect a level of biodiversity to a specific ecological process.
A common data task gives species counts for two sites and asks you to compare diversity and link it to function. Work through it in order.
Compare species richness
Count the species at each site. A healthy kelp reef with 24 species has far higher richness than an urchin barren with 6 species. Always state both figures.
Judge evenness
Check how individuals are spread. The healthy reef has individuals spread fairly evenly across many species; the barren is dominated by a single urchin, so its evenness is low. High richness and high evenness together mean high species diversity.
Link diversity to function
Translate the comparison into function. The diverse reef has functional redundancy, so it captures more energy, builds more habitat and is more resilient. The barren has lost redundancy, so productivity, habitat structure and resilience all collapse.
State a conclusion
Conclude clearly: the kelp reef is far more biodiverse and therefore more productive and resilient than the urchin barren, which shows how biodiversity loss strips ecological function.
Bringing it together
To answer this dot point well, describe the biotic and abiotic structure of an ecosystem, define the three levels of biodiversity, and then explain, with a Tasmanian example, how that diversity underpins productivity, stability and resilience. Use the kelp forest collapse or the Tasmanian devil to show what happens when biodiversity is lost.
Biodiversity is not just a count of species. An area with five common species and one rare one is less diverse than one where individuals are spread evenly across six species. Always mention both richness and evenness for species diversity, and remember the genetic and ecosystem levels too.
Exam-style questions
Questions in the style of TASC exam questions on this dot point, each with a worked answer. They are written by ExamExplained unless tagged "Past paper"; the year shows the paper a question is modelled on.
Practice8 marksA survey of two Tasmanian east-coast reef sites recorded the following. Site A (healthy kelp forest): 24 species, with individuals spread fairly evenly. Site B (urchin barren): 6 species, dominated by one urchin. Using the data, compare the biodiversity of the two sites and explain how the loss of biodiversity at Site B reduces ecological function.Show worked answer →
An 8 mark data-and-explain question rewards a quantitative comparison plus a function link.
Compare using the data. Site A has far higher species richness (24 vs 6 species) and higher evenness (individuals spread fairly evenly rather than dominated by one urchin), so Site A has much higher species diversity. Quote both numbers and name both richness and evenness.
Explain the loss of function. With only six species and one dominant grazer, Site B has lost functional redundancy, so few or no species can take over the roles (habitat building, primary production by kelp) that the lost species performed. Energy capture falls, habitat structure is gone, and the food web has fewer alternative pathways, so the barren is less productive and far less resilient to further disturbance.
Markers reward the richness-and-evenness comparison with figures and the redundancy-to-resilience link.
Practice6 marksExplain, using the three levels of biodiversity, why a population of Tasmanian devils with low genetic diversity is especially vulnerable to Devil Facial Tumour Disease.Show worked answer →
A 6 mark explain question wants the levels linked to a specific function.
Genetic level. Low genetic diversity means there is little variation in immune-system genes across the population, so few individuals carry resistance and the disease spreads through almost the whole population by biting.
Species and ecosystem levels. As devil numbers crash, species diversity falls and the loss of this top predator ripples outward: feral cats and other species can increase, changing the wider community and reducing ecosystem-level diversity and function.
Markers reward connecting low genetic variation to a weakened immune response, then extending the loss to species and ecosystem levels.