Starter

Find your data from the practical that we did before the holidays.

You have 10 minutes to:• Complete the graph using the checklist to make sure

that it is up to standard• Make a quick conclusion and evaluation based on your

analysis

How does this experiment represent Natural Selection?

Ecosystem stability – learning outcomes

• You should all be able to:– Identify that a more stable and complex

ecosystem is likely to have more diversity.

• Most of you should be able to:– Explain the link between diversity, ecosystem

stability, succession and habitat.

In pairs…

• Discuss how you think diversity changes with the following factors:– Succession– More complex food webs

• Write down your ideas

Complexity of the ecosystem

Look at these food chains from two different ecosystems. Which do you think would be more resilient to the loss of a species? Why?

http://www.ecoshape.nl

http://taksnoproblem.pbworks.com/w/page/24225677/Food%20Webs

Succession• When plants and animals

colonize a bare piece of land (secondary) or bare rock (primary) there are few species at first.

• Species diversity increases with time until a climax community is reached when species composition is stable (able to maintain equilibrium).http://www.teara.govt.nz/en/forest-succession-and-regeneration/1/1

http://sciencebitz.com/?page_id=41

Diversity may fall throughout the process of succession, due to a disturbance.

Communities in young ecosystems that are undergoing succession may be more vulnerable to these disturbances than the older ones which are more resilient and stable.

http://sciencebitz.com/?page_id=41

Ability of ecosystems to recover

Three factors determine an ecosystem’s ability to recover from disturbance:

1. Inertia (persistence) – the ability of an ecosystem to resist change when subjected to a disruptive force

2. Resilience – ability of a system to recover after change or a disturbance

3. Diversity – the number and proportions of species present

In pairs, discuss the following questions…

• Explain why a climax community is more stable than a pioneer community.

• Explain why a complex ecosystem is more resilient to change.

• Explain why monocultures have low inertia (easily disrupted) and low resilience (struggle to recover after a disturbance).

http://oegardens.com/gardening-in-polycultures/

http://www.worldbiomes.com/biomes_grassland.htm

Single species crops (monocultures) such as the corn crop here have low inertia (easily disrupted) and low resilience (they struggle to recover).Why?

In contrast, natural grasslands may appear to have only one species but they contain a variety. Although they have low inertia and may be easily disturbed (e.g. burning) they are very resilient, due to nutrient-rich soils, and usually recover quickly.

http://www.arkive.org/kagu/rhynochetos-jubatus/image-G111700.html

http://web.georgetownisd.org/tippit/MunozA/projects.htm

Tropical rainforest has high diversity and inertia, but if it undergoes catastrophic disturbance through logging or fires it has low resilience.Why?

Complex ecosystems like rainforest have complex food webs which allows plants and animals many ways to respond to a small disturbance. They also contain long-lived species and dormant seeds that promote inertia

http://todayinsocialsciences.blogspot.mx/2010_12_01_archive.htmlhttp://www.tulsaaudubon.org/guides/tallgrass-prairie-preserve.htm

Compare the stability, diversity, resilience and inertia of these three different ecosystems.

North American wheat farmingTall grass prairie – a native ecosystem

to central USA

http://www.arkive.org/kagu/rhynochetos-jubatus/image-G111700.html

Tropical rainforest in New Caledonia

Quick Quiz1. What happens to diversity as succession proceeds?

2. Which is more stable a pioneer community or a climax community? Explain why.

3. Why does a tropical rainforest have low resilience?

4. Suggest one reason why high biodiversity creates greater ecosystem stability.

5. What is the difference between primary and secondary succession?

6. Which of these is generated by human activities?

Learning outcomes

• You should all be able to:– Identify that a more stable and complex

ecosystem is likely to have more diversity.

• Most of you should be able to:– Explain the link between diversity, ecosystem

stability, succession and habitat.