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}