Lecture #6: Community Ecology

Concept of community and basic terms

A population consists of organisms of a particular species and characteristics like natality, mortality, age structure, growth dynamics, and so on. But, when several populations share a common habitat and its resources; they interact among themselves and develop into a BIOTIC ‘community’. Thus a community is a larger unit since it includes more than one species’ population.

A biotic community has its own characteristics:

1. Animal populations sharing a common habitat and interacting among themselves form an animal community, and Plant populations of an area form a plant community.
2. But, the biotic community includes all populations of living organisms of a common habitat, ranging from a tract of forest to the whole forests, from a small pond to a lake and so on.
3. It also exhibits certain distinguishable characteristics, such as – diversity, dominance, density, composition and stratification.

The biological potential of species’ population determines a tolerance range for environmental conditions. The range of environmental conditions which a taxon can tolerate is called the ecological amplitude.

The composition of a biotic community in any habitat is dependant upon the prevalence of environmental conditions in that habitat and the ecological amplitude of species’ populations.

Ecotone

Each community has its spatial limits. Sometimes the boundary between two communities may be very sharp (such as that between a forest and a lake) or gradual (as between a forest and grassland). This transitional zone or junction zone between two or more diverse communities is called ecotone.

The ecotone harbors a community (called an ecotonal community) including organisms of each of the overlapping communities, and in addition, organisms peculiar to it. Generally the number of species and their population densities are greater in ecotones than in the communities flanking it. The occurrence of increased diversity and density of organism at the ecotone is due to the edge effect of two distinct communities.

For example, if man settles in a forest, he reduces the forest to scattered small areas interspaced with grasslands, agricultural lands and other open habitats. If he settles in the plains, he plants trees around his habitation. Thus by his activities, man creates an ecotone – some of the original organisms of the forest and plains survive in the man-made forest edge ad many species of insects, birds and mammals often increase in number in these zones.

Community function

Community (in ecology) is a dynamic system, which changes over time through the functions of community dynamics and succession. Moreover, to add on to this, we have seen that communities are made up of populations which interact with each other in many ways and influence their development over-time.

Ecological succession involves an orderly process of community changes, which are directional and hence predictable. It involves a modification of the physical environment, culminating in the establishment of a stable community. A sequence of temporary communities replace one another in a given site, thus bringing about changes in the physical environment, which in-turn determines the pattern of succession. In other words, succession can be regarded as the changes which increase the community complexity over time.

The transitional series communities which develop in a given area are called ‘sere’ or ‘seral’ stages, while the final stable and mature community is called the climax. Ecological succession is therefore community controlled although the environment determines the successional pattern. Succession is of two types, a).Primary succession, and, b). Secondary succession.

Keystone Species: In many communities one or a few species appear to be very important in maintaining the community structure… these are called “Keystone”

Primary Succession (PS) begins on a sterile area (an area not previously occupied by a community), such as a newly exposed rock or sand dune where conditions for existence may not be favorable initially. PS involves the following stages,

1. Nudation – this is the exposure of the new surface and is followed by the arrival of the propagates/propagules or seeds from a neighboring region through the process called migration.
2. Germination phase – where the seeds and propagules depending on the environmental conditions germinate.
3. Ecesis phase – this is where the seedlings establish themselves on the land’s surface.
4. Full-scale colonization – this is the 4^th phase.

Colonization by successive off-spring and new migrants help increase the population, through a process called aggregation. Plants of organism (autotrophic) which are the first to colonize and aggregate are called pioneers. PS refers to autotrophic succession – which begins in a predominantly in-organic environment, or, succession which takes place when bare, lifeless substrate becomes available for colonization (VERY slow process).

Secondary Succession (SS) refers to community development on sites previously occupied by well-developed communities (the site may be rich in nutrients and hold favorable survival conditions). SS can be regarded as re-colonization following disturbance (much faster than PS). For example, SSs that occur in cut-over forests and abandoned croplands – here, the environment is both in-organic and organic based. Another type of succession occurs on a fallen log or in an aquatic environment (ecosystem) loaded with sewerage. Here the environment is predominantly organic and heterotrophic organisms usually dominate. This type of succession is called heterotrophic succession.

Some salient points regarding SS

A plant community may be disturbed causing some plants to be destroyed, as from a fire or from human logging or cultivation. If the disturbance stops, the community will begin a SS, changes in the vegetation that will lead back to a climax community i.e. the progression of plant communities occurring on areas where there has been previous vegetation (destroyed by fire, farming, or other).

Since the soil is already in place, SS can take place five to ten times faster than PS.

It is important to remember that the abiotic factors (such as weather, humidity, and temperature) affect the nature of the plant community. Also the plant community affects these abiotic factors. Therefore, if a plant community is significantly disturbed, the loss of the vegetation may change the abiotic conditions. If this occurs and the habitat has changed, SS may lead to a different climax community.

What are the main ecological factors makes succession happen?

1. Tolerance: only species which can tolerate full range of conditions survive early succession. Some pioneering species dominate because they have broader “tolerance ranges”.
2. Facilitation- species present change the environment and make it more hospitable for others.
3. Inhibition- species present change the environment and make it less suitable for themselves

An example of ecological succession (PS)

Consider the hydrarch succession or hydro-sere in which a pond and its community are converted into a land community. This could happen in the following stages:

In the initial stage – phytoplankton are the pioneer colonizers. They are consumed by zooplankton and fish. Gradually these organisms increase the content of dead organic matter in the pond. This is utilized by the bacteria and fungi and minerals are released after the decomposition.

The nutrient rich mud then supports the growth of rooted hydrophytes (Vallisneria, Gratophyllum etc) in the shallow water. Thereafter, the hydrophytes die and are decomposed by microorganisms thus releasing nutrients.

Besides, some dead organic matter lies in the mud, gradually reducing the margin of the pond, which is occupied by species whose leaves reach the water surface and roots remain in the mud (nelumbo, nucifera, Trapa spp, monocharia spp etc, grow in these conditions.

Gradually the water depth in the pond decreases due to evaporation and the decomposition of organic matter, and the concentration of nutrients increase.

Free floating plants like lemna, pistia etc increase in number because of the high nutrient availability. Gradually their dead parts fill up the pond bottom, which gets raised. The pond becomes (then) a swampy ecosystem. The reed species invade the pond and are gradually replaced by mesic communities as the water depth is reduced gradually. Thereafter, gradually land plants invade.

In association with the changes in water depth and vegetation the aquatic fauna also change and ultimately gets replaced by land animals.

Consider the case of natural water reservoirs that may be found in some plateaus and valleys. Hydrosere arising in these aquatic environments usually leads to the establishment of deciduous forests.  A possible trend of succession in the aquatic environment can be summarized as follows.

Xerosere or xerarch secession

This begins on exposed parent rocks (lithosere) or drysand (psammosere). The pioneer plants are lichens, mosses, selagnella, which help in the soil formation by accelerating erosion. In course of time, grasses, animals and herbaceous vegetation grow on the soils deposited on rocks. Later the mixed woodland species (e.g. ficus etc) appears. In saline areas, the sere is called halosere.

An example of PS for a forest habitat that can happen on a barren rock

1. Bare rock is first colonized by lichens and bacteria.
2. Small amount of soil formed by the lichens is colonized by mosses, which do not have roots and require little soil, and ferns.
3. As the seedless plants live and die, the soil continues to develop to the point that grasses can successfully grow and a grassland community forms.
4. Over time, the soil level increases to the point that shrubs can grow in the grassland.
5. The grassland is replaced by a shrub community.
6. The shrub community may be gradually be replaced by a forest.

Lichens (pioneer species) à  mosses and ferns à grasses à shrubs àtrees…

In this example, please note that each stage alters the habitat in such a way that it prepares the way for the next invasion of species. As succession proceeds, soil is formed and thickens – the result of decomposition.

When the changes in the composition of plants stop and the plant community remains generally the same for many years, the community is mature or at climax. A climax community is the relatively stable community at the end of succession.

Dynamic trends in succession

Some structural and functional changes which occur in the process of succession can be grouped/categorized as follows:

1. Species composition – a change in the species composition occurs. The change is fast in the beginning and then is more gradual.
2. Species diversity – some plant species which were present in the initial stages may not be found in an advanced stage of succession. However, in the climax stage – there may be more kinds of autotrophs and heterotrophs than in the earlier seral stages.
3. Density and biomass of organisms – there is usually a marked increase in the number (density) of organism. The number may decline in the latter stages, but in the climax stage the biomass structure remains very high. The total biomass gradually increases and reaches a maximum in the climax stage.
4. Heterotroph population – the number of species usually goes on increasing as the food chain relationships become more complex in the climax stage.
5. Chlorophyll – green pigments go on increasing during the early phases of PS. The ratio of yellow/green pigments remain around 2 in the early stages and increases to 3 to 5 in the climax stage. Pigment diversity also increases.

Functional Changes during succession

There is a progressive increase in the amount of living biomass and dead organic matter. There is an increase in grass as well as net primary production in the initial and seral stages. Thus there is more biomass accumulation, gradually reaching a huge biomass structure in the climax stage.

The food-chain relationships become more complex as succession proceeds. Researchers have established that the stability of the climax community is associated with high species diversity, large accumulation of the living bio-mass and complex food chain relationships. Figure below summarizes the changes in biomass and primary production that can occur through the passage of succession.

The community respiration increases but the P/R ratio (‘production to respiration’ ratio) remains more than 1 in the seral stages. The huge living biomass respires a lot in the climax stage and the P/R ratio equals 1 (P:R = 1). Thus in the early stages P>R, and in the climax P = R. Refer to figure below.

The complexity of the climax community increases number of ecological niches and the routes of flow through the system. These attributes make the climax community more stable. Furthermore, it has also been established that productivity increases from poles to the tropics, and hence it may mean that a climax tropical forest is more stable than a temperate climate deciduous forests (and, so on).

The climax concept in ecological succession

Many theories (to date) have been put forward by ecologists to explain the climax concept such as,

1. The mono climax theory,
2. The poly climax theory, and
3. The Information theory.

1. The mono climax theory

Clements (1916), was of the view that in a given climate, the successional stages (seral stages) will ultimately end up as climatic climax vegetation. If this to be true, succession is a progressive phenomenon. The emphasis is on the fact that only one type of climax vegetation develops.  This is called the mono climax theory. But some communities like savannahs/prairies with grass land climax (in Canada, USA, Africa etc) also prairies, shrubs and forest patches in low areas in the mesic belt as stable vegetation.

Ecologists supporting the mono climax theory argue that this vegetation is post climax. But others feel that the post climax concept is confusing. It has also been observed that different types of stable vegetation occur within the same climatic belt. Yet other plant ecologists consider this vegetation pre-climax. Pre-climax vegetation is that which has not reached the climax stage due to the prevalence of some adverse climatic, topographic and edephic environmental conditions. Due to human activites, such as cutting, fire, grazing and so on, the successional process may be checked and the community may not reach the climax stage. However, some sort of stable vegetation may develop under such circumstances. Such vegetation is called dis-climax or post climax.

2. Poly climax theory

Looking a the occurrence of several types of climax vegetation (in Europe), Braun-Blanquet (1932) proposed the polyclimax theory, which states that there may be climatic climax, edaphic climax and biotic climax depending upon the situations in which the climax vegetation has developed.

Therefore, succession may not always be progressive. In course of succession, a community with longer life forms like forests may be degraded and patches of grass land may occur within them (retrogressive succession)

Note: the two above said theories explain the climax concept from a structural view point. However, looking at the problem/case of succession from an energistics point of view is also possible (since energy drives all functions in a community or in an ecosystem). This has led to the development of the ‘information theory’ – to explain the concept of the climax community.

3. Information theory

In this the community is considered a thermodynamic unit. It receives energy from the sun and concerts it into chemical energy from the sun and converts it into chemical energy, performs its activities and dissipates heat energy. In the seral stages, the dissipation energy is usually less than the input energy – therefore there is more of net production, and the community grows. In the early stages, the species diversity is low and the food chain relationships simple; but in the course of scission the total information in the community increases (i.e. the food chain relationships become more complex and the possible interactions between individuals, species and materials increase).

In the climax community the input energy is more or less equal to the output energy (particularly) the dissipation energy), which makes for negligible NPP.

Time factor in ecological succession

Ecological succession is dependent on the time factor even though it is often taken for granted.  For example, consider the foll cases; primary succession on sand dunes or recent lava follows takes about 1000 years.

Secondary succession on abandoned agricultural land in a tropical climate taken about 100 years; whereas for a moist temperate climate – it is 200 years

Secondary succession in grasslands (as per the observations/experiments in North America by ODUM in 1966) take about 50 to 60 years to reach a climax grass stage – this occurs in 4 distinguishable stages,

1. 2 – 5 years of annual weed stage,
2. 3 – 10 years of short-lived grass stage,
3. 10 – 20  years of perennial grass stage, and,
4. The climax grassland stage – reached in some 20-40 years.

Significance of ecological succession

The principles and trends of ecological succession indicate that seral stages are more productive, although comparatively less stable. The climax community is nature and stable with greater biological diversity, larger becomes structure and balanced energy flow and is able to buffer the physical environment. This community provides man with food, fuel, fodder, medicine and so on and is able to control the climate and keep a balance with regard to biogeochemical cycles. It is (as such), considered a multiple use system – since the P/R ratio in such a community is – there is not much NPP for harvesting. Since the fast growing human population needs a huge amount of food and other materials – man is forced to look for high NPP systems – which decreases that he needs early successional stages as a source of food.

Disturbances to ecosystems and the continuous cycle of succession

Disturbances (either by natural or anthropogenic means) are an integral part of some ecosystems, e.g. forest fire destructions are part of the dynamics of eucalyptus forestland in Australia. Any event that interrupts life in an ecosystem is (can be) defined as ‘disturbance’.

If there is no further manipulation of the system after the disturbance an ecosystem will slowly (gradually) develop and reach its climax stage. But, when there are intermittent shocks, the climax stage will not be reached and a lesser stable community dominating the system is also possibility to be considered. For example, think about the case-study on the grasslands in Batticaloa you have taken up for ENS 2133. Can you relate that example with SS?  Please consider the diagram below as a ‘thought-provoker’.

Why is it important for us to understand the concepts behind succession?

As a budding environmental scientist, you need to know, that:

1. Natural systems can maintain themselves, whereas disturbed systems cannot.
2. Human influence on succession can be positive or negative – generally, humans knock out the climax community.

An interesting example of human interference with succession = producing a green, weed-free football ground (or lawn). Producing such a lawn means a constant battle against natural plant succession

1. What you must do to maintain such a system
   1. plant grass seed – these are needed to complete against natural seed dispersal of many different species,
   2. mow – this limits the establishment of trees and other tall species,
   3. apply herbicides – to eliminate inter-specific competition (competition between different species) and to cut down on species diversity – must be done because broad-leaved species are often more adaptable and successful than grasses and can out-compete them,
   4. apply fertilizer – grass species use up soil nutrients quickly (particularly when clippings are bagged),
   5. irrigate – natural rainfall is often inadequate for lawn grass,
   6. apply fungicides and other chemicals to control disease and insect pests- must be done because an unnatural ecosystem (such as a lawn) is more prone to disruption.
2. Thus, when humans interfere with plant communities – many problems that would normally be controlled in a natural systems occur at a blown-up level (this is same thing happens in farming).
3. Without the continued interference of humans, the yard would have a natural sequence of succession over time.

Summary

We have seen the various aspects of ecological succession, and why it is an inevitable phenomenon in ecology. As student of environmental science, you should be able to correlate the theoretical elements behind this phenomenon to understand the natural environment, and to manage the environment sustainably. Knowing when and where ecological succession can be manipulated, gives you the power to design and improve ecosystems for the benefit of the human society (e.g. Coppock et al., experiment of 1993 in Africa). However, the ethical aspects of manipulating the natural environment should be given careful consideration before taking any drastic action to modify the natural composition(s).

Lecture #5: The Niche

A Summary of previous lectures:

Ecology (scope, definition/s, functions, need)
System/s concept
Basic components
Resistance/resilience
Adaptation
Tolerance limits
Trophic levels – food chain relationships
Bio-geochemical cycles…

Expected Learning Outcomes of this Segment/Lecture:

1. Understanding what a niche is…
2. Ability to apply niche concept to explain competition, speciation and evolution…

[Important Keywords: niche, resource, limiting similarity, stability, equivalent]

What is a niche?

Defined as “the range of environmental factors over which an individual can have positive fitness” (for an organism/species).
Describes the environmental factors to which an organism has adapted… adaptation can be understood in the context of the niche structure!

Niches have two components:

1. The ABIOTIC component – elements of the physical environment that affect the fitness, survival, or reproduction of an organism

2. The BIOTIC component – interaction with other organisms (i.e. competition, symbiosis etc.) that can affect the organism’s fitness

The fundamental niche:

Biotic factors limit the contextual space occupied by an organism and result in a (fundamental) niche. Competition with other organisms for the factor determining the fundamental niche can be super-imposed in it…

Zonation

The influence of abiotic and biotic factors on species distributions can lead to zonation, or the bands of species replacing each other across the environmental gradient…

Niche: the eco-questions…

1. Can two species ever share the same niche?
2. Is that possible?
3. How much differences must be there between the niches of two species before they can co-exist in the same locality?

To know the answer, one should realize, that a NICHE is…

1. Limited by the resource, and, space…
2. Time is a ‘factor’…, and,
3. Finding the answer will yield info on how many species can be packed into a single environment…

Competitive Exclusion, explained by Hutchinson

The ratio of the larger to the smaller species must be no smaller than 1.3 (or ≈ ‘cube-root of three’) for the two species to have sufficiently distinct niches to allow co-existence…

Inference to Hutchinson’s rule

“Body mass or volume must differ at-least by a factor of 2 between species competing for food in-order for them to be able to survive and co-exist in the same location…”

Character displacement

“Selection due to competition will act to increase the size difference between two species – with the larger becoming even larger and the smaller even smaller…”
However, max and min sizes could also be constrained, due to the size diversity of the prey they feed on…

Ecological equivalents

Are organisms that occupy the same or similar ecological niches in different geographical regions… may be taxonomically different, but will be performing similar eco-functions… e.g. kangaroos and antelopes!

Bio-diversity and community function

1. Species diversity contributes to community stability
2. Ecosystem services increase with species diversity…
3. Changes in ecological time… affects bio-diversity and community function
4. So is the change(s) in geological time…

Homework/Practice Qs

Q1. Is it logically possible for a species to exist in more than one niche?
Q2. Explain how speciation can occur using the niche concept…
Q3. How can you correlate Q1 with Q2?

–The END of Lecture #5–

Lecture #4: Adaptation(s), Convergence and Divergence…

Adaptation…

Environmentally induced – if, short term; it is non-genetic!
Stable adaptations are always based on genetic changes… and have evolutionary bases…

Theories by:

1. Precht (1958) – defines RESISTANCE ADAPTAIONs as adaptations which give rise to plastic resistance. Some adaptations not only prevent injury but also permit growth – these are called CAPACITY ADAPTATIONS by Precht.
2. Prosser (1964) – defines physiological adaptation as any property of an organism which favors survival in a specific environment, particularly a stressful one…

Physiological Adaptations

These non-genetic adaptations are helpful to a particular organism/individual in its lifetime…
On the other hand, genetic or evolutionary adaptations help the species face competition, survive and reproduce…
An adaptation is considered to be genetic or stable if it has an evolutionary base.
A stable adaptation usually develops in the course evolution, and is carried on from generation to generation.
Non-genetic adaptations may not be stable and are physiological in nature…

Convergence and Divergence

Under similar environmental conditions, different species (i.e. unrelated species or taxa) exhibit similar features. This is called convergent evolution.

Example: fish (poikilothermic) and whale (homeothermic) belong to different taxa. But, despite these differences, these exhibit common morphological features – these are adaptations required for aquatic living.

On the other hand, individuals belonging to a particular taxon, as in reptiles or mammal, may adapt to different environmental conditions. Depending upon the demands of their environment, they develop different adaptive features in the course of their evolutionary history. This is known as DIVERGENT EVOLUTION.

Rules on CONVERGENT and DIVERGENT evolution…

1. Allen’s Rule – Tails, bills, ears etc. of animals a relatively shorter for a species in cooler regions.
2. Bergmann’s Rule – Races of species having a larger body size are generally found in the cooler parts of the range while those having a smaller body size are found in warmer parts. This is applicable to both cold and warm-blooded animals.
3. Gloger’s Rule – In homoeothermic species, black pigments increase in warm and humid habitats and red and yellow brown pigments in arid climates. These pigments are greatly reduced in cold climates.

Another example of the Gloger’s Rule…

Large body size and smaller appendages… cold climates; preventing heat loss!
But, (not necessarily) a relatively lower surface area will not imply cold adaptation in Homeotherms… it is also dependant on adaptive strategy, insulation of the body surface…capacity for higher rates of heat production… and, ability to tolerate cold temperatures at the tissue level(s).

Responses to change in the environmental complex

1. Masking – this refers to a modification of one factor by the another…
2. Directive – it refers to the environmental factor bringing about a definite type of orientation in the animal.
3. Deficient – any deficiency of an environmental factor in a particular habitat may affect the activity or metabolism of the animal.
4. Lethal – an environmental factor may cause death, as for
5. Controlling – certain factors may influence the rate of occurrence of some physiological process without entering into the reaction.

Threshold of an environmental factor

Is the minimum quantity of that factor required for the functioning of an organism…
For example, it may be the lowest temperature at which the organism remains active…
As such, an environmental factor has a certain range within which the species remains active and performs all functions optimally…

Tolerance ranges of species are normally determined genetically… as per their evolutionary pathways!

Steno = narrow range of tolerance
Eury = wide range of tolerance

i.e. stenohaline, and, euryhaline… stenoecious, and, euryecious

Where,
Haline = salinity (i.e. tolerance to salinity); Ecious = context of habitat/niche

Law of Minimum

In the natural environment, an organism is simulatenously subject to the influence of many environmental factors… such as temperature, RH, pressure, O2, PH of the medium etc… Some factors exert more influence than the others…

Justus Von Liebig (1840) developed the concept of the LAW OF THE MINIMUM by evaluating the relative role of these factors.

LAW OF THE MINIMUM = organism requires a minimum quantity of a particular nutrient for proper growth!

Your tasks…

1. Write down the summary of what you have learnt in this lecture…
2. Refer and write a small synopsis on the applicability of the ‘law of minimum’ in ecological processes…
3. Look at http://www.ens2112.wordpress.com for information regarding your course work…

Lecture #3: Impact of Biological Stress and Strain at the individual level in ecosystems

A recap of previous lecture and its continuation…

A body/entity remains in a state of STRAIN if subjected to stress. 

A body/organism is considered sensitive to a stress if a little stress is required to produce a unit strain. Magnitude of STRESS can be measured as the ‘FORCE/Unit Area’.
Magnitude of STRAIN = measured as the CHANGE in DIMENSIONS… (i.e. changes in the length, volume of the body)
Each body has certain LIMITS of CONTINUING in a state of strain.

Elastic and Plastic Strain

A completely REVERSIBLE strain is said to be an ELASTIC STRAIN.
If a strain is PARTIALLY reversible, then the IRREVERSIBLE part is called PLASTIC STRAIN or PERMANENT SET.

Elastic Strain

The ELASTIC STRAIN produced by a body is proportional to the stress applied on it, where,
Elastic Strain –directly proportional –> STRESS
The modulus of elasticity (M) of the body is defined as:
M = (Stress)/(Strain)
A higher M implies more elasticity!

Biological Stress and Strain

(In biological sciences) the concept of stress always involves the possibility of the occurrence of an injury, implying that the strain is IRREVERSIBLE.
All living organisms possess a barrier (cell membrane, cell wall, epidermis etc.) between the living matter and the stress, and usually their energy is expended in COUNTERRING this stress.
Biological Stress may be defined as any environmental factor capable of introducing an INJURIOUS STRAIN in organisms.

Biological Strain

… is not necessarily a change in the dimension of an organism.
Organisms exhibit physical strain through hybernation/aestivation or through shifts in metabolism.
Aestivation? Earth worms aestivate during summer by forming distinct coils or by remaining very TORPID.
When (biological) strain is SEVERE = organism may suffer a PERMANENT SET (INJURY), where the ultimate Permanent Set is DEATH (PLASTIC STRAIN)…
Resistance of an organism to stress may be compared to ELASTIC STRAIN…

Elastic and Plastic (biological) strains

ELASTIC RESISTANCE is a measure of the organism’s ability to reduce or prevent plastic strain (irreversible or injurious).
For biological stress or strain, TIME is a very important criterion… since death or injury is generally dependant on the duration of exposure to stress.
In ORGANISM’s plastic strain increases with the increase in the intensity of stress. The organism may repair the strain (injury) by expending METABOLIC INJURY… if strain is so severe or irreversible that the organism dies.

Stress resistance depends on the…

1. Physiological State of the organism
2. Healing or repair mechanism which reverses the strain
3. Capability of the organism to adapt to the environment

Adaptation and the Concept of the limiting factor…

What are adaptive strategies? Why do we need them?

Environment acts as a selective force – and those with the right adaptive strategies survive… prosper!
E.g. Hydrophytes, xerophytes

Adaptations to environmental temperature…

Case study of Regulators = Homeostasis… “homeotherms”! AND,
Conformers = Poikilotherms

Adaptation…

Stable adaptations are always based on genetic changes… and have evolutionary bases…

Theories by:

1. Precht (1958)
2. Prosser (1964)

Your task…

• Comment how various environmental stresses can determine the distribution of a particular species using a suitable example…

Lecture #2: Organism and the environmental complex

The natural environment in which organisms live has two components:

1. Abiotic – characterized by physical and chemical factors – i.e. temperature, rainfall, pressure, Ph
2. Biotic – all living organisms, which interact with each other…

Interactions:

It is the interactions between the biotic and abiotic components in an ecosystem that define and determine its existence. From an organismal perspective, we can broadly categorize two types of intercations.

1. Organisms interact with members of their own kind/species = INTRASPECIFIC interaction
2. Organisms also interact with members of other species = INTERSPECIFIC interaction

Interactions in an ecosystem could be in the form of parasitism, symbiosis, intra- or inter-specific competition, and predator~prey relationships. Interactions helpful to the organism are classified “positive” and vice versa…

Interactions are IMPORTANT for survival, growth, reproduction and the CONTINUANCE of any species. 

An organism lives in a state of dynamic equilibrium with the environment. As the (natural) environment is in a constant state of flux, the organism has to continuously make adjustments.

These ADJUSTMENTS are made in response to external changes in one or more environmental factors (i.e. concentration of atmospheric O2/CO2, temperature, relative humidity, Ph etc.)… and, are extemely necessary for an organism to be able to survive, grow and reproduce…

“Adjustments are necessary for the continuity of an organism’s own life and for the continuity of life of its own kind (species)…”

The organism’s environment:

Any organism, regardless of its size or function, has two environments:

1. The internal environment, and,
2. The external environment.

Both the internal end external environments of an organism are continuously interacting through the epidermis/cell membrane/cell wall…

The ORGANISM needs to maintain a stable internal environment irrespective of its external environment. This property of living things is called as ‘homeostasis’… and is an important aspect of the evolutionary process. Along the evolutionary pathway, as the organisms evolved from single-cellular biological entities to multicellular and complex organims such as mammals etc – the homeostatic ability of organims have also increased.

The “ORGANISM~ENVIRONMENTAL COMPLEX”:

Ecologists are faced with the challenge of understanding the organism-environmental complex and the strategies adopted by different species for their survival and continuance. Different species have different genotypes (genotype = sum total of all genes possessed by an organism.

Species differ from one another appreciably, exhibiting  different strategies and homeostatic mechanisms in response to environmental changes and interactions, because they possess different genotypes. Each genotype expresses itself in the form phenotypes, with regards to its structure and functions. Depending on the variation in environmental conditions (it is very likely) that one genotype will have a number of phenotypes.

An interesting example:

Consider the case of Europeans being larger (i.e. broader and taller) than the average Sri Lankan. Though Europeans and Sri Lankans are of the same species (i.e. Homo sapiens sapeiens) and are of Caucasian origins – seperated by geography and time, why do they differ in size?

Eurpoeans being the phenotype in a colder climate need to conserve body heat to maintain temperature homoeostasis, whereas Sri Lankans living in a warmer climate need to loose heat to cool their homeostasis. Heat loss in an entity (organism) is proportional to the ‘SURFACE : VOLUME’ ratio.

Sri Lankans tend to be small thus reducing ‘volume’ to maintain a high SURFACE/VOLUME ratio and Europeans tend to be big and have high ‘volumes’ to maintain low SURFACE/VOLUME ratios.

Environmental factors and ‘interactions’:

The environment includes a number of factors and the interactions between them. An environmental factor is considered important if it has the following features:

1. It is operationally significant to an organism’s functioning and living processes
2. It is effective sometime during the life of an organism
3. It is ontogenically effective.

As per Mason and Langenbein (1957)  and Vernberg and Vernberg (1970)– a functional concept can also be applied to the environment – where the natural environment can be: organism-directed, organism-timed, organism-ordered and organism-spaced…

Dash (1993) uses a CONCEPTUAL model (developed on the basis of a standard parabolic survival curve) to decribe the zones of tolerance and resistance for an organism with regard to environmental factors – this can be used to explain the total range of expression of/for an abiotic factor by an organism/species.

The concept of ‘stress’ and ‘strain’:

Common Definition of STRESS:  “Any environmental factor potentially unfavorable to organisms is called as STRESS”.

An organism’s ability to survive in a particular environmental complex depends on its evolutionary history. RESISTANCE to stress is defined as the ability of living organism to survive and grow in the presence of unfavorable factors. If a body X exerts a force on body Y, then Y must also exert a ‘counter force’ on X.

In Newtonian terms these are called as ACTION and REACTION. Taken together,  ACTION and REACTION may be called STRESS.

YOUR TASKS:

1. Scientists speculate that the age of large reptiles (i.e. the dinosaurs) in the past history of Earth came to a full-stop – when there was ‘sudden climate change’. The Earth’s climate which was favorable and warm, suddenly ‘twilted’ and became extraordinarily cold – paving way for the ice-age. This was the time when the early mammals came into existence. These creatures – thanks to their smaller sizes; survived and contributed to the ‘age of mammals’ and the composition of organisms of the Earth at present. Using your knowledge on the surfcae:volume ratio concept as well as what you know regarding ‘homeostatic abilities along the evolutionary pathways’  – comment on this speculation by scientists.
2. Please list the topics/sections that have been taken-up for discussion in Lecture #2 (so far).

{END of LECTURE #2}

Lecture #1: Introduction to Ecology

Logical Quetions:

It is quite logical and necessary to ask the fundamental question… “What is ecology?” before starting to learn ecology… We can go on to ask 4 more sub-questions… such as –

1. How do we define ecology?
2. What do ecologists do?
3. What are ecologists interested in?
4. Where did ecology emerge from in the first place?

Please note that sub-questions #1 and #4 are related as ‘how ecology as a discipline has originated’ will determine ‘how it is being defined’…

Some background information:

Ecology (originally in German: Oekologie) can lay claim to be the oldest science.

First defined by Ernest Haeckel (1866) as – “the comprehensive science of the relationship of the organism to the environment.”

It was Burdon-Sanderson (1893) who discussed various sub-disciplines of science defined ecology as – “the science which concerns itself with the external relations of plants and animals to each other and to the past and present conditions of their existence.”

Ricklefs (1973) defined ecology to be – “the study of the natural environment, particularly the interrelationships between organism and their surroundings”.

However, the disturbing fact is that all the previously said definitions seem vague since they tend not to address neither the physiological nor the morphological aspects of plants/animals…

This made Andrewartha (1961) to add a new term into the definition – “INTERACTIONS”!!!

And, obviously… (as it is expected) – zoologists, botanists and other sectoral specialists deviated to form definitions for ecology as per the scope and needs of their respective disciplines…

The COMPREHENSIVE definition of/for ecology:

And, as per Townsend et al., (2000) the comprehensive definition of ecology should essentially focus on aspects that explain:

1. Where the organisms are found?
2. How many occur there?
3. Why???

Thus, Townsend et al., (2000) define ecology as: “the scientific study of the distribution and abundance of organisms and the interactions that determine distribution and abundance.”

Moreover, it is to be noted that… There is applied and pure science – as such, the question is: “where does ecology fall into”?

Is it an applied science or a pure science?

Applied = problem solving, management perspective (highly practical and not so ‘bookish’ i.e. academically inclined)

Pure = quantifying, determining, truth seeking (tends to be sometimes of very less practical value)

There can be no definite answer to this… But we know un understand that ecology being concerned (or focusing entirely) on the natural environment, needs to take in facts:

1. That the environment is complex,
2. And, canNOT be understood in a singular (linear) perspective…
3. There, are many unanswered questions re: environment
4. Yet the need to understand and comprehend is IMPORTANT for our survival

As such, focused questions are necessary from the ecologists if they are trying to understand  and explain ecological phenomena.

Explaining about systems/phenomena/entities in a scientific manner:

Explanations can be proximate or ultimate.

Where, proximate explanations focus on ‘what is going on here and now’. And, ultimate explanations focus on providing discussions on what has happened, what is happening, and, what is bound to happen – using evidence that has been accumulated historically etc.

Furthermore, when trying to explain what is to happen – ecologists predict what will happen in the future…

All this is necessary for managing the environment in an optimal sustainable manner (i.e. to see whether control without exploitation is achieved).

How is it DONE in ecology?

When posed with the question: ‘how ecology is practiced’? We need to focus on –

1. How understanding is achieved?
2. How this understanding can help us predict, manage, and control the environment?

The fundamental points that need to be understood about doing (or practising) ecology (as a profession) are, that:

1. Ecological phenomena occur at a variety of scales (time and spatial).
2. Ecological evidence comes from a variety of different sources.
3. Ecology relies on true scientific evidence and application of quantitative methods (essentially statistics).

What is essentially addressed by the discipline of ecology?

The discipline of ecology addresses environmental relationships (i.e. between organisms and the physical environment from those of individual organisms to factors influencing the entire biosphere).

These broad range of subjects can be organized and facilitated by arranging them as levels in a hierarchy of ecological organization…

As per biological components there are (traditionally) four levels in the ecological hierarchy of organization:  i.e. individuals –> populations –> communities –> ecosystems!

Moreover, with the present trends in visualizing the Earth as a singular living entity – one can add biosphere as the fifth and the highest biological (entit-al) level.

BUT, WHAT SHOULD BE UNDERSTOOD IS…

That, as per the most comprehensive definition – ecology focuses on the investigation of the interactions between the biotic and abiotic components of the world/Earth. As such, we should consider the non-living physical and chemical components of the Earth also as part and parcel of the hierarchy of ecological organization.

For example –

|<————- Earth System Level ——————>|

Biosphere –> Region –> Landscape –> Ecosystem –> Community –> Interactions –> Population –> Individuals

Note that the study of “(interactions, populations and individuals)” = intra-community level investigations!!!

Some Definitions:

• Environment:  this means everything in the surroundings of an organism that could possibly influence it.
• Habitat:  a habitat is where an organism lives i.e. where it obtains its food and shelter, and where it reproduces.
• Population:  the (total) number of individuals of a particular species in a defined habitat (or given area).
• Community: a community is made up of all the plants and animals living in a habitat.
• Ecosystem: the community of organisms in a habitat, plus the non-living part of the environment (air, water, soil, light etc.) make up an ecosystem.

Individuals of the same species = POPULATION,

POPULATION + Populations of other species = COMMUNITY,

COMMUNITY + non-living part of the environment = ECOSYSTEM!

For example, a population of carp forms part of the animal community  living in a habitat  called a lake. The communities in this habitat, together with their watery environment , make up a self-supporting ecosystem. Or, to put it in other words, an ecosystem can be regarded as a self-supporting community plus the physical features of its environment. The Earth’s surface containing living organisms (i.e. the biosphere) can be considered as one singular and vast ecosystem or a collection of many inter-twining ecosystems…

NATURAL and ARTIFICIAL ecosystems:

Natural ecosystems – [Many examples of these have already been discussed. They may be ponds, rivers, lakes, woods, grasslands, forests, peat bogs, or dune systems to name just a few. These are self-supporting (and self-regulating), needing only sunlight, air, water and mineral nutrients to survive. They usually contain a wide range of interdependent plants and animals and need no inputs from humans.]

Artificial ecosystems – [Ecologically these are not very exiting but are essential to the human survival for they constitute of the farms, gardens, plant nurseries, agro-forestry plots, parks and/or domestic gardens. For example, on arable lands plants of a single species are introduced and grown in dense stands specifically for their food or other commercial value to humans. In these systems, the manager attempts to abolish food chains and food webs that could be present in the natural environment – so as to conserve energy, and for making control easy. Unless carefully managed, these could do long-term harm to their own and other environments.]

The SCOPE of ecology:

Ecology is usually considered as a branch of biology, the general science that studies living organisms. Organisms can be studied at many different levels, from proteins and nucleic acids (in biochemistry and molecular biology), to cells (in cellular biology), to individuals (in botany, zoology, and other similar disciplines), and finally at the level of populations, communities, and ecosystems, to the biosphere as a whole; these latter strata are the primary subjects of ecological inquiry.

Ecology is a multidisciplinary science. Because of its focus on the higher levels of the organization of life on earth and on the interrelations between organisms and their environment, ecology draws on many other branches of science, especially geology and geography, meteorology, pedology, genetics, chemistry, and physics.

Thus, ecology is considered by some to be a holistic science, one that over-arches older disciplines such as biology which in this view become sub-disciplines contributing to ecological knowledge.

In support of viewing ecology as a subject in its own right as opposed to a sub-discipline of biology, Robert Ulanowicz stated that “The emerging picture of ecosystem behavior does not resemble the worldview imparted by an extrapolation of conceptual trends established in other sciences”. Agriculture, fisheries, forestry, medicine, and urban development are among human activities that would fall within Krebs’ (1972: 4) explanation of his definition of ecology: “where organisms are found, how many occur there, and why(?)”.

Ecological knowledge such as the quantification of biodiversity and population dynamics has provided a scientific basis for expressing the aims of environmentalism and evaluating its goals and policies. Additionally, a holistic view of nature is stressed (as necessary) in both ecology and environmentalism.

Deep Ecology and Ecosophy:

Deep ecology is a recent branch of ecological philosophy (ecosophy) that considers humankind an integral part of its environment. Deep ecology places greater value on non-human species, ecosystems and processes in nature than established environmental and green movements.

Deep ecology has led to a new system of environmental ethics. The core principle of deep ecology as originally developed is Arne Næss’s doctrine of biospheric egalitarianism — the claim that, like humanity, the living environment as a whole has the same right to live and flourish.

Deep ecology describes itself as “deep” because it persists in asking deeper questions concerning “why” and “how” and thus is concerned with the fundamental philosophical questions about the impacts of human life as one part of the ecosphere, rather than with a narrow view of ecology as a branch of biological science, and aims to avoid merely utilitarian environmentalism, which it argues is concerned with resource management of the environment for human purposes.

The PRINCIPLES of DEEP ECOLOGY:

1. The well-being and flourishing of human and nonhuman life on Earth have value in themselves (synonyms: intrinsic value, inherent value). These values are independent of the usefulness of the nonhuman world for human purposes.
2. Richness and diversity of life forms contribute to the realization of these values and are also values in themselves.
3. Humans have no right to reduce this richness and diversity except to satisfy vital human needs.
4. The flourishing of human life and cultures is compatible with a substantial decrease of the human population. The flourishing of nonhuman life requires such a decrease.
5. Present human interference with the nonhuman world is excessive, and the situation is rapidly worsening.
6. Policies must therefore be changed. These policies affect basic economic, technological, and ideological structures. The resulting state of affairs will be deeply different from the present.
7. The ideological change is mainly that of appreciating life quality (dwelling in situations of inherent value) rather than adhering to an increasingly higher standard of living. There will be a profound awareness of the difference between big and great.
8. Those who subscribe to the foregoing points have an obligation directly or indirectly to try to implement the necessary changes.

YOUR TASKS:

1. Please list the topics/sections that have been taken-up for discussion in Lecture #1..
2. Write a mini-report discussing the various sub-disciplines that will come under ecology. Your report should also include diagrams, definitions, flowcharts etc. and should also be accompanied by a ‘reference list’. Plagiarism will not be tolerated! [This will be a mock-tutorial excercise, and is given to you as a means of polishing up your writing skills. This will be taken up for discussion on the 10th/11th of November 2009].

Practice-Questions:

1. What communities might be present in a woodland?
2. Answer both parts comprehensively: a). What is the habitat of an earthworm?  and, b). What makes up the environment of an earthworm?
3. Name some of the producers, consumers, and, decomposers that might be present in a grassland ecosystem?
4. Plants make their food by photosynthesis, so in what ways can they be said to ‘compete for food’?

Disciplines in Ecology:

Ecology is a broad discipline comprising many sub-disciplines. A common, broad classification, moving from lowest to highest complexity, where complexity is defined as the number of entities and processes in the system under study, is:

• Palaeoecology deals with organisms and their environment in the geological past.
• Ecophysiology examines how the physiological functions of organisms influence the way they interact with the environment, both biotic and abiotic.
• Behavioral ecology examines the roles of behavior in enabling an animal to adapt to its environment.
  Population ecology studies the dynamics of populations of a single species.
• Community ecology (or synecology) focuses on the interactions between species within an ecological community.
• Ecosystem ecology studies the flows of energy and matter through the biotic and abiotic components of ecosystems.
• Pollution ecology deals with the movement of pollutants in the environment, environmental deterioration, and the maintenance of its cleanliness and ambient quality.
• Systems ecology is an interdisciplinary field focusing on the study, development, and organization of ecological systems from a holistic perspective.
• Landscape ecology examines processes and relationship across multiple ecosystems or very large geographic areas.
• Evolutionary ecology studies ecology in a way that explicitly considers the evolutionary histories of species and their interactions.
• Political ecology connects politics and economy to problems of environmental control and ecological change.
• Resource ecology deals with renewable and non-renewable resources and their judicious management.
• Conservation ecology deals with the application of ecological principles to the proper management of resources leading to the sustainable management of the environment/biosphere.

Please note that, another recent classification by Dash (1993) characterizes that ecology can be broadly categorized into two spheres, namely organism-based studies and Habitat based studies…

–THE END–