Ecology

Ecology

Ecology is the study of the relationship of living organism with each other and their nonliving environment.

The study of ecology helps us to understand and improve agriculture, forestry, fisheries, and conservation.

Biosphere
This is part of the earth where life exists.
The biosphere is subdivided into areas of unique environmental conditions called biome. Largely the biosphere is divided into terrestrial and aquatic biomes

Based on rainfall and temperature terrestrial biome is further subdivided into

(i) Tropical rain forests that are hot [24-28⁰C ] and wet throughout the year

Due to good environmental conditions animals do not need special adaptations, however, plant exprience high competition for light

(ii)Temperate deciduous forest which winter in a half the year and hot the other half

The major problem in this biome is that half of the year is winter when the temperature is too low for life. To survive in this condition, organisms have developed the following adaptations.

1. loss of leaves by the trees in winter to reduce on water loss by guttation.
2. small animals hibernate
3. birds migrate to tropics during winter
4. some animals have accumulated a lot of fat to prevent heat loss in winter
5. some have short life cycle in of 3-6 months and survive in dormant stage in winter

(ii) Deserts that are hot and dry throughout the year

To survive in the desert organism have developed the following adaptations.

•  Small plants and animals have got very short life cycle; For instance, plants may germinate, mature, flower in a few weeks following occasioned rainfall and then survive in form of seeds during the long dry spell.
• To overcome shortage of water, the camel; use metabolic water and its body is very resistant to dehydration; certain frogs can survive for years without water by burying themselves deep into the sand. When it rains they dig themselves out, mate and lay their eggs in shallow puddle. Here the tadpole grows very quickly, metamorphosing into adults before the puddle disappear.
• The camel has got broad feet not to sink in sand.
• Some plant such cactus store water in their fleshly stems.

(IV) Tandra have long winters and short growing seasons.

Factors that affect distribution of organisms on earth include abiotic and biotic factors.

Abiotic/environmental factors that affect distribution of organism on land

1. Soil
It provides vital link between the biotic (living) and Abiotic (nonliving components) of the terrestrial ecosystem.

Qualities of good soil depend on

– Size and nature of inorganic particles
– Amount of water available
-soil air
– Presence of humus and organic matter
– Soil pH
– Soil temperature
– Dissolved mineral salts

2. Climate
Climate refers to the predictable long-term pattern of rainfall, temperature and light. Weather is more short term. It may be cold, windy and wet one day and warm, calm and dry the next.

Elements of climate are
(i) Rainfall; areas with much rainfall thought the year contain more living organism that those that do not
(ii) Sunshine/light
Effects of light on living organism
– Photosynthesis in plant
– Photoperiodic behavior in plants i.e. influence flowering in plants
– Phototropism
– Phototaxis
– Vision in animals
– Migration of animals
– Reproduction

(iii) temperature
most organism survive between 0 -40⁰C though, some thermophilus [heat – loving] bacteria can complete their entire life cycle at temperature in excess of 100⁰C.

(iv) Relative humidity
This the measure of the amount of water vapor in air. Low humidity lead to high evaporation that may cause dehydration of organism.

Hot and humid climate may be harmful because reduced evaporation prevents cooling of organisms.

(v) Wind.

• Occasional stormy wind can flatten trees that are 100 years old.
• Continuous strong wind can prevent trees from becoming established.
• Wind serves a useful function in the pollination and seed dispersal in plant
• Migratory birds may use winds to minimize.

(ii) Air;

Contains oxygen for respiration  and carbon dioxide for photosynthesis.

(iii) Fire
Fire may result from light, volcanoes and human setting fire.

Ecological effect of fire
– kill slow animals & plants
– some animal migrates
– encourage soil erosion &leaching
– release poisonous gases
– encourages regeneration in some grasses e.g. Cymbopogon
– destroys or chase away vectors, pests and parasites, e.g. tsetse flies
– accelerates nitrogen recycling of plastic waste.
– Enable vision of distant are for prey and predator.
– Allow growth of fire resistant species which are often not palatable.
– Destroys humus

(iv) Topography

Topography means altitude, slope and aspects of a place.

This affects distribution of organisms by determining the amount of rain, light, humidity and wind.

Factor that affect distribution of organisms in water include

(i) Salinity affects osmoregulation in animals;

animals that can osmoregulate may live in both fresh and seawater while those that cannot are restricted to the sea.

(ii) Nutrient availability
The most important nutrient in water are the nitrates and phosphate. Lake with low phosphate and nitrate (oligotrophic) contain more species than lakes with high levels of nitrates and phosphates (eutrophic lakes)

In eutrophic lakes, the high levels of nitrates and phosphate promotes high growth rates of algae and other photosynthesis organism. This in turn support large number of aerobic bacteria which decompose the dead photosynthetic organisms. However, the aerobic bacteria take up more oxygen from water thus oxygen concentration may fall below that, can support life of big organism.

(iii) depth of water
shallow water is not able to support big animals like whales

(iv) how permanent is the water body
temporary water bodies do not support organisms that live permanently in water

(v) tide strength

Very strong tides prevent the growth of plant near the lake and big animals in water and water body shores

 

Biotic factors
These include ways by which living organisms influence the distribution of others through interspecific and intraspecific associations.

Intimate associations include

Parasitism;
A parasite is an organism that lives on or in another organism from which feed. A parasite which lives on the surface of its host is called an ecto-parasite and that lives inside it’s called an endo parasite. Most species, including human, harbor parasites that reduce their health and may cause death.

Challenges faced by a parasite
Locating a new host
Overcoming host rejection
Entering a host

Parasitic adaptations
Parasite show many different adaptations of overcoming these challenges, depending on whether they are ecto-parasites or endo-parasites.

• Many endoparasites show degeneration, or even total loss of certain organs which reduces their energy and material requirements and hence a reduced burden on their host. For example, gut parasites like the tapeworms lack an alimentary canal.
• Many parasites especially ecto-parasites have attachment devices such as sucker, hooks or anchors enabling them to cling to the host. Tapeworm has hooks and suckers to anchor on host digestive canal.
• Some parasites have penetrative devices for gaining entrance into the host and its cells. For example, miracidum larva of the liver fluke, has a slender tip on to which open a group of glands which secrete tissue- digesting enzymes. By softening the tissue, the enzyme enables the larva to bore into the foot of a freshwater snail the intermediate host.
• Gut parasite live in a particularly hazardous environment. They typically have protective device which protects their being harmed by the host’s digestive processes. These devices include the possession of a thick protective cuticle, the secretion of large quantities of mucus and the production of inhibitory substances which locally inactivate the host’s digestive enzymes.
• To protect themselves from the host’s immune system, some parasites such as the blood fluke, schistosoma, that cause, bilharzia, synthesizes chemicals, which switch of the host’s immune system; The parasite coat’s itself with molecules which the host recognizes as self.
• Parasite overcome a problem of moving from one host to another by a number of strategies, one of which is to wait until the host mates. The various organism responsible for sexually transmitted diseases in human spread in the same manner
• Many parasites employ a secondary or intermediate host which conveys the parasite from one primary host to another. Thus, the Anopheles mosquito transfers the malaria parasites from one person to another.
• To raise the probability of success vast number of offspring are produced
• The parasites may have a dormant resistant stage in its life cycle to survive adverse conditions until a suitable host is found.
• Some parasites are closely linked with their host that their tissue are actually interconnected.
  E.g., certain plant parasites such as mistletoes plug into other plants and tap off nutrients from the host’s tissue.

Exercise
Which one of the following characteristics of a parasite is not a means of ensuring conti¬nuity of the species of the parasite?
A. Degeneration of redundant body structures.
B. Means of penetrating another organism.
C. Protection against host enzymes.
D. Means of dispersing offspring

The answer is A

• Degeneration of redundant body structures is an adaption of a parasite to it mode of life, but does not directly ensure continuity of its species.

Note :some of the adaption of a parasite that ensure continuity of the parasite species include

• Possession of penetrative devices for gaining entrance into the host.
• Possession of protective devices which prevent the parasite from being harmed by the host’s digestive processes. For example, gut parasites inhibitor substance which inactivate the host’s digestive enzymes.
• Having a means of dispersing its offspring. For example, employing a secondary (intermediate) host which disperses the parasite over a wide area.
• Producing a large number of offspring to increase the chance of success in getting from one host to another as is the case in a parasitic fungus and malaria (plasmodium) parasite
  Production of chemicals which protect some parasite against the host’s defense mechanisms.

Commensalism
This is a relationship between two organisms. One of the two organisms, the commensal benefits from the association, while the other organism usually the larger partner, neither lose nor gain.

Mutualism; Here the association benefit both the participant, i.e., the gain is mutual. E.g. lichen is an association between a fungus and an alga. The fungus absorbs water from atmosphere while an alga photosynthesizes for both.

Predation
In this relationship in which one organism lives the other dies instantly. For example lion the predator kills the zebra (prey) instantly.

 

Energy transfer; food chains and trophic levels.
Within the ecosystem the energy- containing organic molecules produced by autotrophic organisms are the source of food [material and energy] for heterotrophic organisms; a typical example is a plant being eaten by an animal. This animal may in turn be eaten by another animal, and in this way energy is transferred through a series of organism, each feeding on thepreceding organism and providing raw materials and energy for the next organism. Such a sequence is called a food chain.

Definition
A food chain is a sequence of organisms with arrows pointing from organisms being eaten to organism that eats it.

Each stage of the food chain is known as a trophic level, the first trophic level being occupied by the autotrophic organisms, the primary producers. The organism of the second trophic level are called primary consumer, those of the third level are secondary consumer and so on. There are usually four or five trophic levels and seldom more than six because;

-There simply not enough energy in ecosystem to support more than this number of steps. As it is, top carnivores often have to roam over huge area to find enough food.

-It is difficult to imagine a species with the hunting abilities necessary to feed on eagles, loins, killer whales or any other existing top carnivores,

-The more levels in food chain the less stable it becomes.

Food webs
Is feeding relationship showing organisms feeding on more than one organisms.

Ecological pyramids
Food webs give a useful description of the feeding relationships in a community. However, they are non- quantitative. Feeding relationship and energy transfer through the biotic component of ecosystem may be quantified and shown diagrammatically as ecological pyramid. These give an apparently simple and fundamental basis for comparing different ecosystem, or even seasonal or variation of pollution induced charged with a single system.

Pyramid of numbers
These are pyramid drawn base on the number of organism in each tropical level it’s based on ideology that preys are usually smaller and more numerous than their predators.

However, pyramid of numbers, despite their name, need not always be pyramidal in shape. Consider the situation where a single very large producer, such as tree, supports a large number of primary consumers. In this case an inverted pyramid of numbers result.
Inverted pyramids of numbers can also result when a community contain parasites. Imagine for instance, a mammal infected with tick or fleas. These parasites are in a trophic level above the mammal, yet their numbers will be greater. Some of inverted pyramids of numbers are shown below.

 

Pyramid of biomass
This a type of ecological pyramid base not on numbers but biomass. Here instead of counting the number of individual at each trophic level. The total mass (biomass) of organisms at each level is measured. The rectangles used in constructing the pyramid then represent the masses of organisms at each trophic level per unit area or volume. The greatest mass is usually found with the producers, but measurement of the biomass at the various trophic levels in the community may also give an inverted pyramid. For instance, at certain times of year, the biomass of the tiny herbivorous organisms that float in lake and oceans (zooplankton) may exceed the biomass of the tinny photosynthetic organisms (phytoplankton) on which they feed. This is because biomass refers to the mass of organism present a particular moment, the so- called standing crop. At this time of the year phytoplankton are able to support the zooplankton due to high rate of turnover than that of zooplankton.

Pyramid of energy
This is the most fundamental and ideal way of represent relationship between organisms in different trophic levels. A pyramid of energy shows the transfer or flow of energy through a community. As a result, pyramids energy are expressed in units of energy per area per time e.g., kilojoules m-2yr-1. A generalized pyramid of energy is shown below.

Consequently, the number of trophic levels in a food chain or the length of the food chain is limited by the energy wasted as it is transferred from organism, i.e. by the efficiency of energy transfer between trophic levels

Other factors are the availability of sufficient food of the preferred types and territorial space

Cycling of matter and flow of energy in eco system.
In almost all ecosystem, the organisms fall into three nutritional groups.
producers
Consumers
Decomposers

These are related as follows;

Organic material synthesized by the producers are eaten and assimilated by the consumers, all the organic materials incorporated into the bodies of the consumers are eventually broken down into inorganic materials. These are then rebuilt into organic compound by the synthesis activity of the producers.

Although matter circulates repeatedly around an ecosystem, this is not the case with energy. Instead, energy is continually lost from ecosystem as heat energy. The photosynthetic producers transfer some of the radiant energy of sunlight to chemical energy in plant carbohydrate. By their respiratory activities the producer, consumer, and decomposers transfer this energy to ATP, whose subsequent hydrolysis provides energy for the cells vital activities. Both in the formation of ATP and subsequent usage, a proportion of the energy is lost from an ecosystem as heat energy. Ultimately, all the energy in an ecosystem is transferred to heat energy. However, the continual trapping the energy of sunlight by green plant compensate for this loss and maintains the flow of energy.

Nutrient cycle.
In order for organisms to maintain themselves, grow and reproduce, they need supply of elements of which they are made. These they regenerate from the cycling of matter or nutrient cycle.

Carbon cycle.

Nitrogen cycle

 

Nitrogen fixation process in order of magnitude.

1. industrial fixation e.g., Haber process
2. mutualistic blue- green bacteria e.g., Rhizobium e.g. legume
3. free- living blue- green bacteria e.g. Azobacter, clostridium
4. Action of lighting etc. on oxygen and nitrogen.

2. Which of the following is the correct sequence representing the action of nitrifying bacteria?
A. Nitrites — nitrates — ammonium salts.
B. Ammonium salts — nitrites — nitrates.
C. Nitrites — ammonium salts — nitrates.
D. Ammonium salts — nitrates — nitrites.

Lesson 2 of 2

Population and niche concept
Population.
A population is group of individuals of the same species in a defined area. The number of individual in a population is called the population size e.g. all Tilapia living in a lake, all fleas on a dog, lion (in a National park). It is important to estimate the population in a given area.

Importance of estimating the population size

• To be able to construct food webs and chains, pyramid of numbers, biomass and energy
• To understand the existing food relationship within a habitat.
• To observe population changes with time/seasons to understand the way population affect each other at different environmental factors.
• To know the population of pests in order to work out control method.
• For management purpose i.e. Plan for cropping programs in game and national parks.
• To value and conserve biodiversity/ natural reserves/ wild life and national parks.
• To understand dispersal/spread of organisms
• To understand the impact of population in the environment.

Estimating population size.
Factors to be considered to select a method to be used.
(i) Size of the organism e.g. big organisms such elephants are easily counted directly
(ii) Mode of the organism such as
Motility; plants and sessile or slow-moving organism may be counted directly, while indirect methods may be required for fast- moving organism in large open grass land.
(iii) Association between organism- some methods such as capture – recapture method requires organism that associate randomly.
(iv)Hostility hostile organism may require special gadgets for collection and/or counting.

(v) Size of the area under investigation. For big area, population may be estimated basing on samples
(vi) Climatic condition
(vii) Topography
(viii) Nature of vegetation

Method for estimate of population size of large animals living in unconcealed habitats, e.g. Antelopes, Hippopotami, lions etc.

Direct counting method using a low flying aircraft.
Basic requirements are an aircraft, survey map of the area and a counter

Procedure
The aircraft is flown on a transect section of the area of a known dimension and the animals in each transect are counted. The aircraft is then flown back along another adjacent transect and counting continues until the whole a rea is covered. Several counts are made and an average is determined. The estimated population in a given unit area is determined.

Advantage

• The method gives a quick estimate of the population of animal in an area.
• It can also be done concurrently with studies on other aspect of population like feeding habits
• It reduces the risk of attack from aggressive animals
• It reduces the risk of counting the same organism more than once
• There is no disturbance to the environment.

Disadvantage

• It is sophisticated and expensive
• Aircraft may scare away some animals to be counted
• It cannot be applied to small animals in concealed habitats such as forest.
• It is greatly hampered by climate; i.e., cannot work in cloudy or mist climate.

 

Aerial photography
Basic requirement are aircraft and good camera

Procedure
Photographs are taken from a low flying aircraft usually on scale over the whole study area. They are developed and animals counted from the photographs. As in direct counting method, a population density is a given number per unit area

Advantages and disadvantages are similar to those for direct count using an aircraft

Drive and count

In this method, animals are driven by a number of people into a particular spot and counted.

Advantage

• it reduces the chances of counting animals more than once
• gives accurate results
  Disadvantage
• it can’t be used on aggressive animals
• it is tedious on fast moving animal
• it is difficult to apply on animals that do not live in herd

Strip census
In this method animals are counted a long path while walking or in a vehicle. The population density of an area is determined as the number per unit area (of strips)

Advantage

• It gives a quick estimate of the animal population of an animal
• It is cheap

Disadvantage

• Some animals such paths and are unavailable for counting
• People of vehicle may scare away the animals
• Fist moving animals may be counted more than once

Direct counting (Census)
Large organisms that are not aggressive and are living in open habitat e.g. buffaloes, Elephants and trees in the forest are counted one by one.

Advantage

• Quick and accurate
• More than one population can be estimated at the same time
• Other aspects of an organism ecology, behavior can be taken at the same time.
• There is minimal disturbance to environment.

Disadvantage

• It may be difficult to count overcrowded acid organism, e.g. flock of weaverbird.
• Some organisms avoid being seen.
• Difficult to use on animals that concealed in their habitat.
• Bad weather may affect visibility and hence the count.
• Does not take into account the immigrants
• Tedious

Determining the population of small animals

Quadrat

Suitability: plants, immobile or easily caught animals

This a small area marked out for study. A quadrat flame (1m2) is thrown randomly and the number of organism within a number of quadrats that represent a known fraction of the total area determined to estimate the total number in the whole area by simple proportion multiplication.

This method provides a mean of calculating three aspects distribution.
Species density. Number of organism per unit area; limitation. It’s time consuming to count each and every individual in a quadrant

Species frequency; this is a measure of the probability [chance] of finding a given species with any one throw of a quadrat in a given area. The limitations are quadrat size, plant size and spatial distribution [random, uniform or clumped].

Specie cover; this is a measure of the proportion of the ground occupied by the species and give an estimate of the area covered by the species as a percentage of the total area. Limitation it is slow and tedious.

Advantages of quadrat method

• Accurate
• Enable the comparison of different areas and species
• It does not have to be completed over a short time
• It reduces the chances of counting same individual twice
• It is possible to estimate population of more than on species at the same time

 

Disadvantages of quadrat method

• In practice animals are not randomly distributed therefore random plots may give inconsistent results.
• Not appropriate for large area
• Not applicable in water and concealed habitat
• Time consuming to do well/tedious
• Causes some level of disturbance to the environment
• Not suitable for fast moving organism

Assumptions

• the quadrats are chosen randomly.
• The organism do not move from one quadrat to another
• The samples taken are representative of the population as whole
• The population is uniformly distributed
• The area of each quadrat should be the same shape
• The quadrate size must be appropriate for the organisms being sampled.

Capture – recapture or mark-release methods.

Here a sample of individual is caught, counted and marked in some ways. Then these individuals are released.

After being allowed to mix with the rest of unmarked population a second sample is caught and the number of marked individual noted. An estimate of population size can then be made from.

Population size = (N x n)/m
Where
N is the number of individuals marked and released
n is the number of individual caught in a second sample
m is the number of marked individual caught in a second sample

Precautions for capture-recapture methods

• Organism should mix uniformly within the population.
• Sufficient time must elapse between capture and recapture to allow uniform mixing.
• There must be no emigration and immigration to the specified area.
• Making does not hinder movement of organism or make the conspicuous to predators.
• Marking should be permanent.

Removal method
The removal method is very suitable for estimating number of small organism particularly insects, within a known area of grass land or volume of water. Using a net in some form of standard sweep; the number animals is recorded and the animal kept. This procedure is repeated a further three times and gradually reducing number recorded. A graph is plotted of number of animal captured per sample against the previous cumulative number of animal captured. By extra plotting the time of the graph to the point at which no further animal would be captured (that is the number in sample = 0) The total population may be estimated, e.g.

From the graph the estimated number organisms is = 425s

Population growth and growth curves

Populations grow and decline in characteristic ways. The size of population increase will be determined by the reproductive potential of the organism concerned and by environmental resistance. A Plot of the number of individuals against time form a growth curve.
Two basic forms of growth curves can be identified by the J-shaped growth curve and the S- shaped or sigmoid growth curves.

The S- shaped or sigmoid growth describes a situation in a new environment:

• initially the population density of an organism increases slowly because there is a shortage of reproducing individual which may be widely dispersed as it adapts to new conditions and establishes itself;
• then increases rapidly, approaching an exponential growth rate. During this growth phase there are optimal environmental conditions- No environmental resistance, birth rate exceeds death rate.
• It then shows a declining rate of increase until a zero-population growth rate is achieved where the reproduction (natality) equals rate of death (mortality).

The declining rate of increase reflects increasing environmental resistance, which become proportionately more important at higher population densities.

In other words, as the number increase, the competition for essential resource such as food or nesting materials, increases until eventually feedback in terms of increase mortality and reproduction failure [fewer mating, stress induced abortion] reduces population growth to zero with natality and mortality in approximate equilibrium.

The J-shaped growth curve describes a situation in which, after initial establish phase (lag phase) population growth continues in an exponential form until stopped abruptly, as environmental resistance becomes suddenly effective. In very general terms the J- shaped growth form may be considered an incomplete sigmoid curve where a sudden limiting effect comes into play before the self- limiting effect within the population assume importance.

The maximum population of an organism that a particular environment can sustain is termed the carrying capacity. This is identified theoretically as the k-value [or upper asymptote] of the sigmoid curve

Factors that affect the size of the population
The number of individuals in a population is affected by four factors; birth, deaths, immigration and emigrations. The change in the size of any population over a period of time can be summed by the equation. Change in the population size = B+I- D- E where
B=birth,

I= immigration,

D=death

E=emigration.

Environmental resistance
The form that the environmental resistance takes depends on the species in question.
Here are the main factors that limit population growth

• lack of food or water
• lack of light
• lack of oxygen
• predator and parasites
• Disease
• lack of shelter
• Accumulation of toxic waste e.g. CO2 and nitrogenous waste
• stress in some case overcrowding may excess stress leading to abnormal behaviors. E.g., Female rats kept in capacity at a high population density show a breakdown in normal maternal behavior, failing to build adequate nest and abandoning their young ones.
• Some biologist argue that in the wild the males of some species of small mammal die prematurely because of excessive stress.
• -Weather and catastrophes. Weather conditions and generally, may drastically reduce population. The effect is perhaps most severe for small organism, but in particularly bad winter even large species may show significant decline in population size
• -Predator -prey relationship; the population of the prey is usually high when that of the predator is low. That of the predator increase with the population of the prey [which provide food]

Survivorship curves
Ignoring for the moment immigration and emigration, birth and death are the two processes which affects population size. However, these processes depend on the age of individuals and on their sex. The crucial factor is the chance of an individual has of surviving to a given age, This can be shown by means of survivorship curve, To understand a survivorship curve, image a population of 100 individuals borne at the same time. The curve shows how many of them are likely to be alive at any particular age. There are three main types of survivorship curve and these are shown below;

Curve (I) is typical of organism such as ourselves that have few young ones. After an initial period of low juvenile mortality, mortality is very low until late in life
Curve (II) is found in many small birds, notice that as the vertical axis is logarithmic, the curve actually shows an exponential decline in the number of individual surviving overtime. The individuals do not die of old that is, there is no senescence.

Curve III The lower curve is typical of many plants and fish. Thousands or millions of young are produced, few of which mature into adults. The vast majority die as juveniles.

The niche concepts
Precise place of an organism and what it does there

The competitive exclusion principle states that two species cannot occupy the same niche in a habitat.

In other words, different species cannot coexist in a community if they are competing for all the same resources.

An example of this principle is shown in Figure below, with two protozoan species, Paramecium aurelia and Paramecium caudatum.

When grown individually in the laboratory, they both thrive. But when they are placed together in the same test tube (habitat), P. aurelia outcompetes P. caudatum for food, leading to the latter’s eventual extinction.

 

Communities
This a sum of all living organism found in a specified. Species within a community interact with each other, sometimes these interactions benefit both species. For example. The fruit produced by the plant supply birds with food, however, the birds disperse the seeds of these fruit which benefits the plant.

Ecosystem
An ecosystem is a self-sustaining unit consisting interacting organisms in area together with the non-living constituents of their environment. Example an oak wood ecosystem consists of living organisms such as trees and animals and the physical environment such as rain, the inorganic components of soil, sunlight and atmospheric oxygen and carbon dioxide.

Succession
This is the change of community overtime that is replacement of some species by other through time.

Primary succession
begins with a bare rock where there is not form of organic matter. Usually the first organism (pioneer community) to colonize a bare rock is the lichen followed by mosses and ferns, big plants and animals as organic matter accumulate. It must be noted that the first organisms to colonize a bare rock must be photosynthetic.

Secondary succession
Occurs when the surface in completely or largely stripped of vegetation but has already been influenced by living organism and has an organic component. For example, a cleared forest or a previous burned or farmed area. Seeds and pores and organs of vegetative reproduction, such as rhizomes, may be present in the ground to influence the succession.

The climax community is often described as having one dominant [those with the greatest collective biomass or productivity] or several co-dominant species

Productivity and biomass
Gross primary production is the total organic material made by photosynthesis in a specified time s known as the.
Net productivity is amount of organic material produced by synthetic organisms actually available to the herbivores since part of gross primary production is respired or decomposed transferred to herbivore or carried downstream.

i.e., Net primary productivity = Gross primary – respired organic matter+ organic matter
productivity decomposed

Trophic efficiency
Is the percentage of the energy at one trophic level which ends up in the next trophic level is called the

A climax community is the final stage of succession, remaining relatively unchanged until destroyed by an event such as fire or human interference.

Environmental carrying capacity is as the population of organisms that can be sustained at a steady state by the resources available in the ecosystem in which they reside.

Deflected succession- A community that remains stable only because human activity prevents succession from running its course. This happens all the time, for example, sheep grazing prevents grassland from developing into woodland

The changes in gross productivity, respiration and biomass during a typical succession is shown below

The figure shows
that in climax community these terms (photosynthetic energy, respiration and biomass) become more or less constant.

An upper limit of biomass is reached when total respiratory losses [R] from the system almost equal gross primary productivity [P], i.e. P/R = 1

The decreased productivity with succession could be due to lock up of the available nutrients in the biomass of the community leading to decrease in available nutrients in the abiotic component of the ecosystem [such as soil and water]

The factors which influence the size of the population in ecosystem

• Natality or birth rate; this is the rate at which new members are added to the population by reproduction. Birth of younger ones increases the population size.
• Mortality or death rate; the rate at which individual die, the higher the death rate, the higher the rate of decrease in the population.
• Immigration rate; organisms moving into the population increase its size
• Emigration rate; organisms moving out of the population decreases its size.

 

• Environmental factors; changes in environment factors affect population size.
• These can be biotic or abiotic.

 

Lesson 3 of 3

Pollution and conservation
Pollution is the damaging release by humans of materials and energy to environment than can be removed by the environment. The materials or energy released are called pollutants.

The pollutants may be biodegradable or non-biodegradable. Biodegradable pollutants like sewage are broken down by micro-organism to harmless substances fairly quickly, whereas non-biodegradable pollutants cannot be so readily broken down. They tend to accumulate and are therefore potentially more dangerous. Below are specific examples

Carbon dioxide
Accumulation of carbon dioxide (from burning fossil fuel, deforestation, etc.) contributes to the global warming or greenhouse effect. The greenhouse is a slow progressive increase in the average temperature of the earth over a time.

The effects of global warming
Melting of ice on mountain tops and earth pole leading to floods
Droughts in subtropical latitude (5-350N)

Causes of increase of carbon dioxide
Deforestation contributes to the accumulation of carbon dioxide, be reducing on the trees that would reduce carbon dioxide by photosynthesis
Burning of fossil fuel and emission of gases from industries add carbon dioxide to atmosphere

Means of reducing carbon dioxide concentration in air
Using alternative source of energy other than fossil fuel such as solar electricity or nuclear energy
More energy-saving measures could be introduced.
Massive tree planting programs to lock up carbon dioxide in the wood
Nutrient enrichment of the oceans might allow huge algal blooms which would trap carbon dioxide in organic matter.

Oil pollution
Oil pollution results in spillage from the petroleum carrying ship. When inevitable accidents happen or when oil refineries are bombed during the time of war. Oil being lighter than water, floats on sea, killing birds and other animals it may also prevent photosynthesis by blocking carbon dioxide.

Methods of treating oil pollution include
Setting fire on the oil
Pumping the oil back into special oil collecting ship
Adding naturally occurring bacteria that can digest oil
Adding special spill cleaners that are relatively nontoxic and biodegradable than previously used detergents.

Damage to ozone layer
Ozone, O3, is found at low concentration in the earth’s stratosphere, 15 to 50km up. Here it protects the earth from dangerous radiations that out damage the cell genetic material leading to cancers. Ozone layer may be damaged by chlorofluorocarbons (CFCs)used as coolant in refrigerators

Pesticides
Pests are organisms which people consider a nuisance or harmful. Pesticide are substances that kill pest.

Qualities of a good pesticides are

• It must be specific
• It must remain for a short time in the environment i.e. easily transform to a non- toxic form
• It must kill the designated population only or should be specific.
• Low toxicity to other organisms
• Cheap
• Readily available

Challenges of using pesticide

• Non-biodegradable pesticides accumulate in plants and animals causing death
• Indiscriminately kill organisms including useful ones including useful ones
• Prolonged use may lead to resurgence of pest because
• May kill natural predators to the pest that we become defendant to the pesticide.

An example persistent pesticide is DDT

Effect of DDT to organism

• it interferes with conduction of impulses in nervous system
• in birds it interferes with formation of egg shell
• reduces sperm count in animals
• DDT has a possible mutagenic effect especially on pests and lead to flourishing of pests on prolonged use.

Biological control

Biological control, the use of living organisms to control pests.

A natural enemy such as a parasite, predator, or disease organism is introduced into the environment of a pest or, if already present, is encouraged to multiply and become more effective in reducing the number of pest organisms.

Qualities of a biological control agent

• Narrow host range. Generalized predators may be good natural enemies but they don’t kill enough pests when other types of prey are also available.
• Climatic adaptability. Natural enemies must be able to survive the extremes of temperature and humidity that they will encounter in the new habitat.
• Synchrony with host (prey) life cycle. The predator or parasite should be present when the pest first emerges or appears.
• High reproductive potential. Good biocontrol agents produce large numbers of offspring. Ideally, a parasite completes more than one generation during each generation of the pest.
• Efficient search ability. In order to survive, effective natural enemies must be able to locate their host or prey even when it is scarce. In general, better search ability results in lower pest population densities.
• Short handling time. Natural enemies that consume prey rapidly or lay eggs quickly have more time to locate and attack other members of the pest population. Small populations of efficient natural enemies may be more effective biocontrol agents than larger populations of less efficient species.
• Survival at low host (prey) density. If a natural enemy is too efficient, it may eliminate its own food supply and then starve to death. The most effective biocontrol agents reduce a pest population below its economic threshold and then maintain it at this lower equilibrium level.

Acid rain
Acid rain is due to releases of acidic gases such as sulphur dioxide (SO2) and nitrogen dioxide (NO2) usually from unregulated industries. Low pH of acid rain is damaging to organism tissues. It causes skin corrosion, and contributes to destruction of forests in Europe and Northern America.

 

Sewage

Sewage is the water-borne waste of society. It includes both domestic and industrial sewage.
Domestic sewage contain human feces and urine, water used to wash these away and dirty water flows from our baths and sinks.

Industrial sewage includes the dirty water from industry, hospital and abattoirs.
Agricultural sewage is not allowed to mix with domestic and industrial waste and is treated separately.

Ecological problems of domestic wastes

• Untreated sewage may end up in water bodies, causing eutrophication.
• Destruction of habitants where they pile
• Bad smell/air pollution
• Leads deadly communicable diseases
• Decay of wastes in absence of oxygen produce methane, a greenhouse gas.

Ways of reducing domestic wastes

• Recycling of non-biodegradable materials in domestic waste
• Burying biodegradable rubbish
• Burning rubbish or treating with chemicals to reduce bulk.
• Use of organic wastes to generate power
• Use of organic waste to produce electricity
• Use of organic waste to generate fuel

Eutrophication
When untreated sewage or agricultural fertilizers enter lakes or rivers, eutrophication may occur.
Eutrophication is enrichment of water with nutrients such as nitrogen and phosphorus.

This leads to overgrowth of algae (or algal blood) which use up oxygen in water leading to death of fish. Death of fish lead to over multiplication of aerobic decomposers, cause further depletion of water and death of fish.

Properties for a suitable chemical to use in water purification

• specific to intended organism
• biodegradable
• toxic to aquatic organism and human life
• unable to change the taste, color or smell of water

Radiation

Radiation from radioactive substance lead to death and or injury of people and animal by causing cancers.

Conservation
This involves managing the earth so as to restore and maintain a balance between the requirements of human and those of other species.

There are two main reasons why we should conserve.
The ethical reason is that we have a moral duty to look after the environment.
The pragmatic argument says that it is to our advantage to ensure the integrity of our environment. If we preserve the tropical rain forest, the greenhouse effect will be lessened; if we conserve fish stock, we get more food from seas, etc.

Revision questions

1. (a) What is meant by eutrophication? (2marks)
   Eutrophication is the heavy nutrient enrichment and low oxygen content of a water body because of excessive discharge of nitrogen and phosphate fertilizers into the water body. It is the presence of higher than normal amounts of nitrates and phosphate in water body coupled with a low oxygen concentration.
   (b) State two human activities that may encourage eutrophication (2marks)
   Excessive use of fertilizers on agricultural land
   Untreated sewage (rich in phosphorus and nitrates)
   (c) What is the effects of eutrophication? (04marka)
   Species diversity decrease and dominant biota change
   Plant, algae and animal biomass increase
   Turbidity of water increase
   Rate of sedimentation increase, shortening life span of the lake
   Anoxic condition may develop
   Less light penetration
   Proliferation of algae, fungi and other aquatic animals due to availability of nutrients

 (d) Effects of eutrophication are more severe in water bodies where thermal pollution occurs. Explain. (2marks)
Warm water has lower solubility for oxygen
High respiration of organism at high temperature reduce oxygen content of water.

2. What is ecological impact of each of the following human activities?
(a) Use of pesticide (6marks)
They are nonspecific and may kill other unintended organisms. This reduces they biodiversity of ecosystem
Most pesticides are persistent. They accumulate along the food chain and may eventually kill/damage other unintended organism at higher trophic levels including man.
Predator of the organism targeted by the pesticide may be deprived of their only source of food and therefore upset the food chain.
Use of broad-spectrum pesticide can lead to pest resurgence after the period of treatment because some pest become resistant yet the pesticide kills the pest and predator.
Pesticide pollute air, water and soil.
(b) Use of artificial fertilizers (4marks)
Fertilizers applied to crop plants are lost in surface run-off water and pollute soil and water resource.
Increase crop yield
Increase nutrient content of the soil
Decrease in the number of microorganisms in the soil such as saprophytic bacteria.
Nitrogen and phosphate-base fertilizers leach into ground water and increase its toxicity leading to water pollution.
They change the chemical composition of the soil.
(c) Over fishing (5marks)
Extinction of some species
Reduction of the population of adult reproductive fish, leaving a population of mainly young individuals because fish caught as soon as they reach catchable size
It may lead to rapid increase in the number of fish prey.
May lead to reduction or even extinction of some aquatic fish predators
Disruption of aquatic

2. (a) Outline the causes of nutrient deficiency in soil (4marks)
Soil exhaustion due to over cropping without intervals of resting of the soil
Leaching nutrients to deeper soil
Excessive use of fertilizers
Water logging
Soil pollution
Burning causes loss of non-metallic nutrients such as carbon
Monoculture
(b) Explain how plants have overcome the problem of nitrogen and phosphorous deficiencies in soils they grow in. (16marks)
Plants living in soil deficient in nitrogen and phosphorus overcome this problem by any of the following means:
Living in symbiotic relationship with organism that are capable of producing such minerals. For example, symbiotic bacteria in the root nodules of leguminous plants fix nitrogen from the atmosphere to nitrates that can be used by the plant.
Some plants live association with the fungi such as mycorrhiza association whereby the fungi digest organic matter, absorb the nutrients and pass them to the plant.
Adopting parasitic mode of feed, to obtain nutrients from another plant that can easily obtain nutrients from deeper soil
Developing long roots that can absorb nutrients that are leached into deeper soil Adopting carnivorous behavior in order to obtain mineral from digested animals such Venus flytrap.

Please download PDF: Ecology (film)

Sponsored by The Science Foundation College +256 753 802709

Thank you

Dr. Bbosa Science