A BRIEF DISCUSSION OF THE PREVIOUS CLASS (5:03 PM)

SPECIES (5:07 PM)

• Introduced Species
• Introduced species have come to be distributed in a particular region because of the role of man, either purposefully or by accident
• The introduced species may not have a negative impact on the local ecosystem unless the introduction has been random
• In many cases, they may actually have a beneficial impact on the local ecosystem into which they have been introduced
• For example, honey bees introduced by man in different regions deliberately have always had a beneficial impact on the local ecosystem by increasing the rate of pollination
• Invasive Species
• These are non-native or alien to the ecosystem in which they are now found
• They always have negative consequences on the ecosystems in which they are alien
• This is because they do not belong to any trophic level in the local food chains and have no functional relations with the life form of that region
• Hence, they become a new source  of depleting the local resources and establish new predator-prey relations, thereby putting pressure on the life forms of the local foodchains
• This can lead to
• 1. Out-competing the local life forms in the use of resources
• 2. Causing forced migration of the local species which not only causes ecological imbalance but also leads to a reduction in biodiversity in the region
• 3. The disturbance of the biotic component will also have an adverse impact on the local habitats
• Cosmopolitian Species
• The range for the cosmopolitan species is found all over the world
• This is because the type of habitat to which they are adapted is found to be present in many regions of the world
• For example, tropical grasslands are found in many continents like South America, Africa, Asia
• Therefore the grassland habitat is available for life forms that have made grassland their home
• Many marine species can be cosmopolitan, cause of the uniformity of the marine environment and also because oceans are interconnected
• Keystone Species
• There are three important properties of Keystone species
• 1. They have a highly specialized niche in their ecosystem. This means they have strong functional relations, with life forms of many trophic levels in those ecosystems
• 2. These have irreplaceability as a property. In other words, if these species are removed no other species can take their place
• They have a strong influence on the entire food web of the region
• Because of these characteristics, the removal of keystone species will always trigger ecological imbalance because of their strong functional ties to many life forms
• Hence, the entire ecosystem in the region comes under pressure including a change in the habitat of that region
• As a result, species in the region may not be able to leave anymore, leading to the ultimate collapse of  the ecosystem
• Keystone species are usually difficult to be identified
• Their presence is only known when the ecosystem begins to develop serious imbalances

PRODUCTIVITY OF THE ECOSYSTEM (6:20 PM)

• It refers to the total energy created and stored by the primary producers particularly the green plant for a given unit  surface area and for a given period of time
• Primary productivity
• This is the rate of production of organic matter by the green plants and by the chemosynthetic producers in a unit period of time for a unit area
• There are two types of primary productivity
• 1. Gross primary productivity is the total organic matter produced by the green plants that include the organic matter used up in respiration by the green plants in a unit period of time in each unit area
• 2. Net primary productivity is the rate of creation of organic matter by the green plants minus what is used by them in respiration
• NPP represents the energy and food available to higher trophic levels and is therefore a true major of productivity
• Secondary productivity
• It is the rate of creation and storage of energy by all heterotrophs in a unit period of time in each unit area
• The highest ecosystem productivity is part of shallow water areas, tropical rainforests, temperate evergreen forests, and regions of intense agriculture
• Intermediate productivity is part of grasslands and is moderately cultivated agricultural regions
• The lowest ecosystem productivity is part of deserts, polar areas, deep sea floors, and wastelands
• Absolute productivity in descending order are:
• 1. Forest (64.5 billion tonnes per year)
• 2. Grasslands (15 billion tonnes per year)
• 3. Continental shelf ( 9.3 billion tonnes per year)
• 4. Cultivated land (9.1 billion tonnes per year)
• 5. Freshwater (5 billion tonnes per year)
• The productivity of continents is 100 billion tonnes per year
• The productivity of oceans is 55 billion tonnes per year
• The productivity of polar is  1.1 billion tonnes per year
• Productivity of ecosystem per meter squared per year:

• Ecosystem	Productivity per meter squared per year
  Reef and estuaries	2000 grams
  Forest	1300 grams
  Freshwater	1250 grams
  Cultivated land	650 grams
  Grassland	600 grams
  Desert	3 grams

BIOGEOCHEMICAL CYCLE (7:12 PM)

• Macronutrients or plant nutrients required in large quantities are  NPK + calcium +magnesium + sulfur
• Trace elements required by plants are cobalt, zinc, manganese, and iron
• The most abundant elements in the lifeforms of the biosphere when all of them are equalized to 100% is
• 1. Hydrogen which comprises 50%
• 2. Carbon which comprises 25%
• 3. Oxygen which comprises 24.8%
• 4. Nitrogen which comprises 0.27%
• Water Cycle
• The hydrological cycle represents the movement of water in the biosphere
• For plants, it is the most important source of hydrogen
• It helps plants to absorb nutrients from the soil and therefore supports nutrient cycles
• It helps in the movement of chemicals needed by different lifeforms
• It is the most expensive consumer of incoming solar energy compared to all nutrient cycles because it alone uses up 15% of solar energy reaching the earth's surface
• Phosphorus Cycle
• Weathering of rocks containing apatite releases phosphate ions into the soil
• These phosphates  are then taken up by plants and from plants, it goes into animals upon consumption
• The animal and plant waste and excreta are converted by bacterial and fungal action into phosphate so that it is available to plants
• These life forms convert organic phosphorus in vegetable and animal waste into phosphates and make it available to plants
• When animal including fish dies, the inorganic phosphorus generated by the micro-organic lifeforms can also be absorbed by sediments of the ocean floor, so that it is again locked up in rocks
• These rocks of the sea floor can be exposed due to tectonic uplift once again exposing the minerals containing phosphorus to chemical weathering

Topics for the next class: Continuation of biogeochemical cycle