Honours / Core Course (CC)
INTRODUCTION TO ECOLOGY
History of ecology
Autecology and synecology
Q.Distinguish between autecology and synecology.
Levels of Organization
Q.Distinguish between system and ecosystem.
Laws of limiting factors
Q.What do you mean by SA:V ratio?
This is a ratio between surface area (SA) to volume (V) of any organism and is a key factor in controlling the uptake of heat and the maintenance of body temperature. As an organism’s size increases, the SA:V ratio decreases. Poikilotherms have low SA:V value in contrast to endotherms.
Q.Write explanatory note on Significance of biological clock
Biological clock is a physiological mechanism for measuring time that couples environmental and physiological rhythms and enables organisms to anticipate daily, seasonal, tidal and other periodicities. An internal biological clock is functional to all living organisms, influencing hormones that play a role in the sleep cycle, metabolic rate and body temperature.
Ecologists are particularly interested in the adaptive value of biological clocks.
a)Biological clock gives the organism a time dependent mechanism. It enables the organism to prepare ahead of time for periodic changes in the environment.
Q.What is daily torpor?
This is the dropping of body temperature to approximately ambient temperature for a part of each day, regardless of season. Some birds such as hummingbirds (Trochilidae), small mammals such as bats, pocket mice, kangaroo mice etc experience daily torpor.
Q.Compare between solar constant and solar flux.
The solar constant (a measure of flux density) is the mean solar electromagnetic radiation (the solar irradiance) per unit area that would be incident on a plane perpendicular to the rays, at a distance of one astronomical unit (AU) from the Sun (roughly the mean distance from the Sun to the Earth).
The solar constant includes all types of solar radiation, not just the visible light. It is measured by satellite as being 1.361 kilowatts per square meter (kW/m²) at solar minimum and approximately 0.1% greater (roughly 1.362 kW/m²) at solar maximum.
This is the amount of radiant energy of all wavelengths that crosses a unit area or surface per unit of time. Only one fifty-millionth of the sun’s tremendous energy output reaches the Earth’s outer atmosphere. Solar flux is estimated to be 1.94c per square centimeter per min (c/cm2/min), for a total of 13 × 1023 c/year.
Study of Physical factors
Unitary and Modular populations
Unique and group attributes of population—
Q. In the given table present a cohort of 530 gray squirrels from a population of Northern West Virginia. From the given life table calculate life expectancy of gray squirrel. (x=represents the age classes and nx=represents the number of individuals from the original cohorts that are alive at the specified age (x).
Information from the table—
Original 530 individuals born (age 0) only 159 survived to an age of 1 year, while of those 159 only 80 survived to age 20. Only 5 individuals survived to age 5 and none of those individuals survived at age 6.
To calculate life expectancy of gray squirrel we need to calculate the following values—
lx=the probability at birth of surviving to any given age (n0/n0, n1/n0, n2/n0 and so on)
dx = measure of age specific mortality (n0 – n1)
qx=age-specific mortality rate (dx/lx)
Lx=average number of individuals alive during the age interval x to x+1 (n0+n1/2)
Tx=total years lived into the future by individuals of age class x in the population (L0+ L1+ L2+ L3+ L4+ L5)
By using the formulae the solution of the given problem is presented in a tabular form as
*lx= n0/n0= 530/530=1; n1/n0= 159/530=0.3
**dx= n0 – n1, n1 – n2
# Lx= n0 + n1/2= 530+159/2= 344.5; n2 + n3/2= 80+48/2=64
@Tx=L0+ L1+ L2+ L3+ L4+ L5
$qx= d0/ n0=371/530=0.70; d1/ n1=79/159=0.50
►Dispersal and dispersion
Q.Briefly discuss the exponential and logistic growth forms.
Two basic patterns based on shapes of arithmetic plots of growth curves can be designated: the J shaped growth form and the S shaped or sigmoid growth form.
(A)J- shaped growth forms—
In this growth form density increases rapidly in exponential fashion and stops abruptly as environmental resistance or another limit becomes effective more or less suddenly.
This growth form may be represented by the simple model based on exponential equation—
dN/dt = rN (b0—d0) N. With a definite limit on N.
r = biotic potential of each individual; b0 = individual birth rate at the beginning; d0= individual death rate at the beginning.
Example—This type of growth pattern can be easily observed in algae blooms, some insects, annual plants and the lemmings of Tundra. (For further information follow contact section)
Q.How logistic model of population growth related to r and k strategies?
The terms r and K used to characterize these two contrasting strategies relate to the parameters of the logistic model of population growth: r is the per capita rate of growth and K is the carrying capacity (maximum sustainable population size).
The concept of r species and K species is most useful in comparing organisms that are either taxonomic or functionally similar.
Growth equation and patterns
r and K strategies population regulation
Q.What do you mean by r and K strategists?
The theory of r and K selection predicts that species adapted to these two different environments will differ in life history traits such as size, fecundity, age at first reproduction, number of reproductive events during a life time and total life span. MacArthur and Wilson (1967) applied the terms
r selected and K selected to populations and this system has been widely used since then.
Species popularly known as r-strategists are typically short lived and having the following features:
i)They have high reproductive rates at low population densities, rapid development, small body size, large number of offspring (with low survival) and minimal parental care.
ii)They make use of temporary habitats.
iii)Many inhabit unstable or unpredictable environments that can cause catastrophic mortality independent of population density.
iv)Some r strategists (e.g; weedy জবুথবু species) have means of wide dispersal, are good colonizers and respond rapidly to disturbance. (for further information follow contact us)
Density-dependent and independent factors
Q4.Give example of impact of density independent factors on population.
In desert regions, a direct relationship exists between precipitation and rate of increase in certain rodents and birds. Merriam’s kangaroo rat (Dipodomys merriami) occupies lower elevation in the Mojave Desert. The kangaroo rat has the physiological capacity to conserve water and survive long periods of aridity. However, it does require the prevailing patterns of seasonal moisture availability to be sufficient to stimulate the growth of herbaceous desert plants in fall and winter. The kangaroo rat become reproductively activate in January and February when plant growth stimulated by fall rains, is green and succulent. This close relationship between population dynamics and seasonal rainfall and success of winter annuals is also apparent in other rodents and birds occupying similar desert habitats.
Q. “Emergence of competition as a central theory in ecology was slow and tentative”—Justify
a)Competition produces less obvious effects than does predation, the development of thinking about competition and its integration into our perceptions of ecological systems have been slow and tentative.
b)Evolution is the expression of competition within populations between individuals having different genotypes (intraspecific competition).
c)Intraspecific competition was implicit in natural selection, interspecific competition left less of an impression on Darwin.
d)Elton discussed interspecific competition only in relation to ecological succession, in which the replacement of one species by a second, having similar ecological requirements, suggested the possibility of interaction between the two. (For further information follow contact)
Q.(a)Mention the name of the yeast Gause used in his experiment on competition. (b)What are the factors in the environment that depress and stop the growth of the yeast population?
(a)Gause (1932) studied in detail the mechanism of competition between two species of yeast, Saccharomyces cervisiae and Schisosaccharomyces kephir
(b)Richard (1928) study in connection to the question—
i)When the growth of yeast stops under anaerobic conditions, a considerable amount of sugar and other necessary growth substances remain in the cultures.
ii)The decisive factors seems to be the accumulation of ethyl alcohol, which is produced by the break down of sugar for energy under anaerobic conditions.
iii)High concentrations of alcohol kill the new yeast buds just after they separate from the mother cell.
iv)Richard showed that the yeast growth could be reduced by artificially adding alcohol to culture and changes in the pH of the medium were of secondary importance. (For further information follow contact)
Gause’s Principle with laboratory and field examples
Q.List out the outcome of Gause’s experiment form a predator-prey cycle of protozoa.
Key : Use completion between Paramecium and Didinium.
Gause’s experiment provides a number of clues about the dynamics of predator-prey cycles in nature.
a)The experiment demonstrate that potential for predator to reduce their prey populations to extinction.
b)Habitat structure may alter the outcome of predator-prey interactions. In the case of Paramecium-Didinium system, the presence of a refuge prevented the predator (Paramecium) from completely eliminating the prey (Didinium). In that case it was the predator population that was eliminated from the system.
c)The maintenance of prey-predator cycles may require interactions on a landscape level. Gause achieved a predator-prey cycle by periodically introducing small numbers of predators from outside the system.
Lotka-Volterra equation for competition
Q.What do you mean by Mathematical model of Lotka and Volterra?
Mathematical models have been used extensively to build hypothesis about what happens when two species live together, either sharing the same food, occupying the same space or preying on or parasitizing the other. The classical models of these phenomena are the Lotka-Volterra equations, which were derived independently by Lotka (1925b) in the United States and Voltera (1926) in Italy.
Alfred J. Lotka
Lotka and Volterra each derived 2 different sets of equations:
(a)Set-I:Applies to predator-prey interactions,
(b)Set-II:Applies to nonpredatory situations involving competition for food or space.
Here we are concerned here only with their 2nd set of equations for nonpredatory competition.
The Lotka-Volterra equations, which describe competition between organisms for food or space, are based on the logistic curve. We have seen that the logistic curve is described by the following simple logistic equations: for species 1,
dN1/dt =r1N1(K1-N1/ K1)---------------------(1)
and for species 2,
dN2/dt =r2N2(K2-N2/ K2)---------------------(2)
Where, N1=population size of species1, N2= population size of species 2, t=time, r1=intrinsic capacity for increase of species 1, r2=intrinsic capacity for increase of species 2, K1=asymptotic density or ‘carrying capacity’ for species 1, K2=asymptotic density or ‘carrying capacity’ for species 2.
In most cases, the amount of resource used by one individual of species 2 is not exactly the same as that used by one individual of species 1.
Lotka and Volterra modified the logistic equation for each species by adding to it a term to account for the competitive effect of one species on the population growth of the other. For species1 this term is αN2, where
α=competition coefficient that quantifies the per capita effect of species 2 on species 1.
Similarly, for species 2, the term is βN1, where
β= competition coefficient that quantifies the per capita effect of species 1 on species 2 (For further information follow contact)
►Ecotone and edge effect
Types of ecosystem with an example in detail
►Detritus and grazing food chains
Q.Distinguish between ‘Grazing’ and ‘Detritus’ food chain in respect of energy flow
►Linear and Y-shaped food chains
Q.Draw a Y-shaped energy flow model and illustrate its components to show flow of energy and its significance.
The grazing and detritus food chains are shown as separate flows in a Y-shaped or two channel, energy flow diagram below—
The Y-shaped energy flow model showing linkage between the grazing and detritus food chains
1.It conforms to the basic stratified structure of ecosystems, 2.Direct consumption of living plants and utilization of dead organic matter is usually separated in both time and space and 3.The macroconsumers (phototrophic animals) and the microconsumers (saprotrophic bacteria and fungi) differ greatly in size-metabolism relations and in techniques required for study.
Significance of the Y shaped model:
i)The grazing and detritus food chains are interconnected, so shifts in flows can occur quickly in response to forcing function inputs from outside the system.
ii)The impact of grazer on the community depends on the rate of removal of living plant material, not just on the amount of energy in the food that is assimilated.
iii)Undergrazing can be detrimental. In the complete absence of direct consumption of living plants, detritus cloud accumulate faster than microorganisms could decompose it, thereby delaying mineral recycling and perhaps making the system vulnerable to fires.
Q.What is consumption efficiency?
This is the ratio of ingestion (I) to production at the next lower trophic level (In/Pn-1) which defines the amount of available energy being consumed.
Example—Sample values of such efficiency for an invertebrate herbivore in the grazing food chain are provided in the figure below. Using these efficiency values it is possible to track the fate of a given amount of energy(1000 kcal) available to herbivores in the form of NPP through the herbivore trophic level.
►Energy flow through the ecosystem
Qa)What is energy? Explain the energy flow with the help of a generalized model, b)Express the principles of food chains and the working principle of the two laws of thermodynamics with the help of a flow diagram.
a)Energy is defined in science as the ability to do work. It is a scalar physical quantity. Although energy is conserved, there are many different types of energy, such as kinetic energy, potential energy, light, sound, and nuclear energy. One form of energy may be converted into another without violating a law of thermodynamics.
A universal energy flow model is applicable to any living component whether it be plant, animal, microorganism, individual, population or trophic group. In the figure as given below the components are:
1.The shaded box B represents the living structure biomass of the component. This Biomass is expressed in calories so that relationships between the rates of energy flow and the instantaneous or average standing-state biomass can be established.
2.The total energy input or intake (I)—For strict autotroph this is light, for strict heterotrophs it is organic food. Some species of algae and bacteria can use both energy sources and many may require both in certain proportions.
Comment:The input flow in the energy flow diagram can be subdivided accordingly to show the different energy sources or the biomass can be subdivided into separate boxes.
3.Other components include— NU=energy not used (stored/ exported), B= biomass, G= growth, E= excreted energy, NA=energy not assimilated by consumers (egested).
b)The energy flow through a trophic level equals the total assimilation (A) at that level which in turn equals the production (P) of biomass and organic matter plus respiration (R).
In the diagram below the boxes represent successive trophic levels and the pipes or lines connecting them depict the energy flow in and out of each level.
i)Here energy flows balance outflows, as required by the first law of thermodynamics and each energy transfer is accompanied by dispersion of energy into unavailable heat (i.e., respiration), as required by the second law.
A simplified energy flow diagram depicting 3 trophic levels in a linear food chain. [I=total energy input, LA= Light absorbed by plant cover, PG=gross primary production, A=a total assimilation, PN= net primary production, P=secondary (consumer) production, NU=energy not used (stored/ exported), NA=energy not assimilated by consumers (egested), R=respiration], S=storage E=assimilated organic matter excreted.
Bottom line in the diagram shows the order of magnitude of energy losses expected at major transfer points, starting with a solar input of 3000 kcal per square meter per day