DP GeographyLecture 18

BiosphereBiodiversity and Change

Syllabus Requirements

• Explain the concept and importance of biodiversity in tropical rainforests. Examine the causes and consequences of reduced biodiversity in this biome.

Biosphere- part of earth where all life exists

If biosphere is a soccer ball, it would be less than half a millimeter thick!

Only about 20 kilometers thick, the biosphere is a shallow layer of soil, rock, air and water

Organic+

InorganicComponents

There are three main sources of energy for the biosphere: GravitySolar radiation- most important as plants do photosynthesis and the cycle goes to other organisms as well Internal Earth forces (ex: plate tectonics, Earthquakes, etc)

An important concept of Biosphere- ECOSYSTEM

According to the Planet Geography book, Ecosystem is defined as “ an interdependent community of plants and animals together with the habitat to which they have adapted”. In a condensed form, it can be defined as a geographical area (variable sizes) where plants, animals, landscape and climate all interact together. All of these factors are interrelated within an ecosystem, and can be indirectly or directly related to other factors of another ecosystem.

Biosphere IS indeed composed by a series of interconnected ecosystems!!

Bear in mind!!Major factor linking different ecosystems together:The Flow of Nutrients and Energy

Rainforest is one of the major ecosystems on Earth !

We’ll go into the topic of biodiversity in rainforests later, but for now let’s look at how an ecosystem work

Cycle of Ecosystem

Ecosystems- flow of energy and nutrients that link the biotic and abiotic environments

1. Energy enters the ecosystem in the form of sunlight that is used during photosynthesis by primary producers/autotrophs (self feeders) such as plants, this is the start of the food chain.

2. Most energy is released by the primary producers, but a tiny fraction of the energy is made available to consumers in three ways: i.) Decomposition, a process in which minerals and nutrients (from decayed organic material such as plant tissues or dead animals) are broken down by microorganisms and are stored in a storage pool for use by other plants ii.) Combustion, the burning of plants releases gases to the atmosphere and ashes to the ground, it can be caused naturally or by human activities such as deforestation iii.) Consumption, primary producers are eaten by secondary producers such as herbivores, which releases the nutrients by both respiration and excretion. Some nutrients are used up by secondary producers as energy but some are stored as animal tissue, which can then be eaten by carnivores, which again releases the nutrients through respiration and excretion. When the carnivores and herbivores die and their remains are not consumed, the nutrients inside are again broken down and released back to the plants.

The flow of energy and nutrients is also known as ‘food chain’

When a plant or animal is consumed by the next consumer within the food chain, most of the energy is lost; Similarly, only one to two percent of the incoming solar energy is converted to plant tissues. As a result, there will be relatively large amount of organisms in the lower stage (also known as trophic level) of food chain to support the consumers above, this is also known as the pyramid of numbers.

Food chains are often composed of no more than 4 trophic levels due to the high loss of energy at each stage, the shorter a food chain is the greater the proportion of energy within the total food chain

But….

• The concept of food chain might be a bit simplified• Some organisms do not just consume one species of

organisms , also there are omnivores (organisms that consume both carnivores and herbivores, humans is a good example) and detritivores (organisms that consume on decomposing organic materials, such as bacteria or fungus)

• Food chains are connected with other food chains, thus it is more realistic to view ecosystem as a complete food web

Limiting factor• Factors that control the stability of an ecosystem• An example: the limited amount of oxygen inside a cave limits the growth

of organisms, which in turn limits the numbers of all other organisms in that ecosystem

Limiting factors may not only be at a minimum level, for instance a factory excretes a huge load of poisonous lead and waste into a river, killing many organisms and disrupting the river’s ecosystem heavily.

There are three critical levels for limiting factors:1st- minimum level- productivity ceases2nd- optimum level- productivity is greatest3rd- maximum level- productivity ceases

Each species within an ecosystem fills an ecological niche, that means they each have a specific role or function within the ecosystem

* A niche might be performed by more than one species, and different animals can adapt to fill different niche!

For example a wolf’s ecological niche might be to prevent the population of sheep to grow too much

Biome

• “The world's major communities, classified according to the predominant vegetation and characterized by adaptations of organisms to that particular environment”, examples are rainforests, deserts, grasslands

• The extent and nature of any particular biome depends on several environmental factors, most notably climate, soils, landforms, etc

• Changeable over time

Biodiversity• Measure of Biome’s resilience (flexibility)• Measure of the variety of life form in biome• Can be described by the number of various species in

a designated area

• “The natural world – biodiversity – provides us with food, materials and energy. We eat animals and plants; insects pollinate many of the foods we consume; microbes in the soil provide the nutrients the plants to grow; vegetation and soil biodiversity reduce flooding and release clean drinking water; vegetation soaks up a substantial proportion of the climate warming carbon dioxide gasses that we emit. The list goes on and on. Urban and rural citizens alike rely on these natural products and benefits.”- Chris Thomas

Biodiversity in RainforestsHot, wet climates is a distinctive feature of rainforests as they exist around or at equatorial areas

Rapid plant growth

Many species compete for nutrients and light in the leeched soils

High biodiversity