#2 Succession

Learning from Nature, from genes to ecosystems

Module 2 Ecological Succession

Core Concepts

Ecology- The study of the relationship between organisms and their environment.

Ecosystem-The biological environment, includes all of the organisms (biotic) living in a given area, as well as the physical components (abiotic) of the environment with which the organisms interact, such as air, soil, water, and sunlight. 

Ecological disturbance-change in “normal” environmental conditions that causes a pronounced change to an ecosystem. Include fires, flooding, windstorm, insect outbreaks.

Ecological succession-the gradual and orderly process of change in an ecosystem brought about by the progressive replacement of one community by another until a stable climax is established.

Overview

Ecological disturbances are a very important and a natural part of ecological processes. They contribute to biodiversity, succession, nutrient cycling, etc. Disturbances such as fire are primarily influenced by climate, weather, and location. Fire disturbances occur in areas where there is low precipitation, ignition (e.g. lightning), and flammable biomass (old dead trees). When there is a combination of long-term conditions (such as drought) followed another factor (such as mis-management of forest land).  Large scale ecological disturbances can cause significant alterations in abiotic and biotic factors. Many plants and animals benefit from the conditions created by disturbances. For example, plants are often said to be the first major disturbance on Earth. The plants that now inhabit terrestrial ecosystems are thought to have evolved from algae. By forming a symbiotic relationship with endosymbiotic bacteria, they were able to begin photosynthesizing (transfer light energy from the sun in glucose molecules, oxygen, and water). This caused a great ecological disturbance. The abiotic environment changed from being a toxic carbon, to the oxygen rich air, which we all enjoy. Change in the air-plants-video about plants changing the atmoshpere

Conditions often occur as part of a cycle and disturbances may be periodic. Other disturbances, such as those caused by humans and invasive species, can occur anywhere and are not necessarily cyclic. When a disturbance occurs naturally, it provides conditions that favor the success of different species over pre-disturbance organisms. This can be attributed to physical changes in the abiotic conditions of an ecosystem in combination with reduced levels of competition. Disturbance can change an ecosystem for a long time. If further disturbance doesn’t occur, many ecosystems will trend back toward pre-disturbance conditions. Such alteration, accompanied by changes in the abundance of different species over time, is called ecological succession. Succession often leads to conditions that will once again predispose an ecosystem to disturbance.

Examples:

·         Prairies

·        

This cyclic pattern of disturbance can be observed in Pine stands in America. Mountain pine beetle (MPB) play an important role in altering pine tree populations, like lodgepole pine in forests of North America. MPB beetles cause extreme devastation to pine stands from Northern Canada to California. There is now evidence, that due to abiotic factors (global warming) MPB is breaching normal barriers and has the ability to cause extreme mortality to trees across the entire North American contentent. MPB exist in endemic and epidemic phases. During epidemic phases swarms of beetles kill large numbers of old pines. This mortality creates openings in the forest for new vegetation. In addition, the older attached tress are susceptible to fire. Interestingly, seeds of the lodgepole pine have adapted to this cycle of disturbance, and only can sprout after a hot burn. Thus, when the canopy is open and there is sufficient light, the young saplings start to grow into the canopy and replace those lost. Younger pines are often able to ward off beetle attacks but, as they grow older, pines become less vigorous and more susceptible to infestation. This cycle of death and re-growth creates a temporal mosaic of pines in the forest. 

A disturbance changes forests significantly. Afterwards, the forest floor contains decaying matter and abundant sunlight promote an abundance of new growth. In the case of forest fires, a portion of the nutrients previously held in plant biomass is returned quickly to the soil as biomass burns. Species, generally plants, are well adapted for exploiting disturbance sites are referred to as early successional species. Vegetation with the potential for rapid growth can quickly take advantage of the lack of competition. Shade tolerant plants (example: ferns and aspen) are able to quickly fill in forest gaps created by fire (or other disturbances). Other plants (cottonwood and silver maple) are well adapted to floodplains. They are highly tolerant of standing water and will frequently dominate floodplains where other species are periodically wiped out. The more complex the plant diversity in an ecosystem, the more animal diversity there is.

Video-Ecology and ecosystem interactions…how plant diversity can influence animal diversity and symbiosis

Now that we have gone over some key concepts and basic processes of ecological succession, Let’s put into practice.

Questions:

A.   Using tools available online, can you describe the differences between the terrestrial ecosystems: grasslands, deciduous forest, taiga, tundra, chaparral, polar ice caps, tropical monsoon forest?

B.    What are the physical characteristics of each

1.     how much rainfall

2.     how much solar radiation

3.     average temperature

4.     average humidity

5.     monthly/seasonal variation in temperature and photoperiod

C.    Biological Characteristics

1.     vertical layering of vegetation (leaf size, crown shape, and tree height)

a.      emergent layer

b.     the canopy layer

c.      the understory layer

d.     the herbaceous layer

e.      the forest floor

2.     Species diversity.

a.      Tropical rainforest and mid-latitude deciduous forest comparisons: plants, herbs, birds and mammals

b.     Why do tropical rainforests have such great biodiversity? http://www.globalchange.umich.edu/globalchange1/current/lectures/kling/rainforest/rainforest.html

c.      Niche specialization

1.     What is an ecological niche?

2.     Habitat specialization.

3.     Feeding specialization.

4.     Camouflage, protective resemblance, and mimicry

Tropical Rainforest Factoids-from teaching about the amazon

• In his book The Diversity of Life, E.O. Wilson reports on finding 43 species of ants on a single tree in Peru. This, he says, is about the same number of ant species as in the British Isles.
• In Indiana, where I live, there are about 54 species of mammals. In Peninsular Malaysia, which has about the same area, there are 100 species of bats alone.
• In Central and South American lowland tropical rainforest there are some 560 species of mammals, more than in all of North America.
• In southwestern Indiana, my Environmental Science class found about 12 species of trees in an area of 0.8 acres. In an area of equal size in northeastern Peru, we might expect to find over 100 species of trees.
• At present, about 1.5 million species of organisms are known to inhabit the earth. Recent studies suggest that there could be 10 to 30 million species in the earth’s tropical rainforests alone. 
• Only about 1% of tropical rainforest plants has been examined for their medicinal properties, but around 25% of our prescription pharmaceuticals come from these very plants.
• Indiana has about 110 species of trees. Dr. Alwyn Gentry found nearly 300 tree species in a one-hectare (2.5 acres) plot in northeastern Peru.
• The Rainforest Action Network estimates that about 78 000 000 acres of rainforest are destroyed each year. This is equivalent to 2.5 acres per second.
• At current rates of destruction, almost all tropical rainforest ecosystems will be lost in the next two decades.
• It has been estimated that tropical rainforest converted to cattle pasture will yield about $150 per hectare. If the forest is cut for timber, it will produce around $900 per hectare. However, if the forest is harvested in a sustained yield manner (fruits, nuts, timber), it will produce an economic value of over $6000 per hectare for years.
• According to The Nature Conservancy, in the year 1500 over 6 000 000 indigenous people inhabited the Brazilian rainforest. In 1992 less than 200 000 remained.