Primary succession on Krakatoa

Succession 2.6.5 student – Krakatoa and class notes and presentation on succession

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In 1997, a professor at Latrobe University in Australia stated that studies of colonization of Krakatau offered “An optimistic lesson: That tropical rainforest ecosystems are capable of recovery from extreme, traumatic damage, if left alone and given time. Within a century the remnant of Krakatau, Rakata, on which not a blade of grass was visible for a year, is now clothed in tropical forest from the shore to its 800-meter peak. On the three islands devastated in 1883 there are now over 400 species of vascular plants, thousands of species of arthropods including 54 species of butterflies, over 30 species of birds,18 species of land mollusks, 17 species of bats and 9 reptiles. And these components of the system have had to cross 44km of sea water to even reach the islands.”

QUESTION: How do colonising species reach and occupy a sterile island like Krakatoa? Organisms colonised the isolated island via several mechanisms. Some seeds have adhesives or barbs to grab onto animals, or have ‘wings’ that allow them to be lifted by light breezes. Fruit-eating animals can carry seeds in their ‘gut’ and ‘deposit’ them on an islands or sterile patches of land.

The process of a changing community:

As a community develops, it alters its physical environment e.g. plant root growth changes the physical and chemical nature of the soil by aerating it and adding exudates (plant liquid waste). The changed environmental conditions which result actually favour the colonisation and growth of different species which eventually give rise to a new community. It is this process of change which is termed succession.

As succession progresses, species diversity and total biomass increase. Eventually, a final succession stage of constant species composition, called the climax community, is reached. The climax community persists relatively unchanged until destroyed by some catastrophic event, such as a fire.

2.6.7 What changes could be influenced by resident species?

1. Substrate (surface on which organisms grow) texture may change from solid rock, to sand, to fertile soil, as rock erodes and the decomposition of plants and animals occurs
2. Soil pH may change from low to higher due to the decomposition of certain organic matter, such as leaves.
3. Soil moisture holding capacity, or the ability of the soil to retain water, changes as the soil texture changes
4. Light availability may change from full sunlight to partly shady, to near darkness as trees become established.
5. Population density changes with population growth and may be unsuitable to certain species.

A good online source for Krakatau information: http://www.bcrescue.org/krakatau.html

View the ‘Crash Course’ video below on Ecological Succession

Take note of the following concepts: disturbances, evaluating the model, change

Table of contents
1. Primary Succession 1:56
2. Secondary Succession 3:36
3. Climax Community Model 5:11
4. Intermediate Disturbance Hypothesis 7:25