Category: ORGANISMS & POPULATIONS Notes

2. Conform: internal environment of conformers changes with external environment

Q:Why small animals are rarely found in polar regions?

A: Small animals have large surface area compared to volume so they lose heat easily in cold and have to expend energy to generate body heat.

But, if stressful external conditions are localized or remain for short duration, then alternatives are migrate / suspend.

3. Migrate: Move from stressful habitat temporarily to hospitable area and return when stressful period over.

E.g.- Migration of birds to Keolado National Park, Rajasthan from Siberia

4. Suspend: Organisms develop mechanisms to deal with stressful situation

Examples- Spores (bacteria and fungi)

– Seeds (angiosperms)- dormancy
– Hibernation (Bears)
– Aestivation ( snails)
– Diapause (stage of suspended development) in zoo plankton

Adaptation

Any ability of an organism that enables an organism to survive and reproduce in its habitat

ADAPTATIONS IN ORGANISMS

1. Kangaroo rat: internal fat oxidation to produce water as by product- concentrated urine
2.Desert plants: thick cuticle, stomata in deep pits to minimize transpiration and special photosynthetic pathway (CAM).  Ex. OPUNTIA – leaves reduced to spines, photosynthetic stems
3. Cold climate mammals: short ears and limbs to minimize heat loss. This is Allen’s Rule.
4. People living at high altitude: increased RBC production and increased breathing rate
5. Desert lizards: bask in sun when cold and move to shade when hot.

POPULATION

Group of individuals living in a well defined area which share or compete for similar resources and potentially interbreed

Example: Lotus plants in a pond

Bacteria in a culture plate

Population ecology is therefore, an imp. area of ecology because it links ecology to population genetics and evolution

POPULATION ATTRIBUTES

1.Birth rate- Average no. of young ones born in  a period of time with reference to the  members of the population.
2. Death rates- Average no. of deaths in a period of time with reference to the members of the population.
3.Sex Ratio- No. of females and males per 1000 individuals
4. Age pyramid: Plot of age distribution (% individuals of a given age or age group)

It reflects whether growth is
(i)            Expanding
(ii)           Stable
(iii)          Declining

POPULATION DENSITY:
Number of individuals present per unit area at a given time.POPULATION GROWTH
Factors affecting change in population density

1. Food availability
2. Predation pressure
3. Weather

Density changes by change in four basic processes
(a)    Natality              –     Increase population
(b) Immigration      –    Increase population
(c)  Mortality           –    Decrease population
(d) Emigration        –    Decrease population

1.Natality (B) : Number of births during given period in the population that are added to the initial density
2.Mortality (D) : Number of deaths in the population during a given period.
3.Emigration (E) : Number of individuals of the population who left the habitat and went elsewhere during the given period
4. Immigration (I) : Number of individuals of the same species that have come into the habitat from elsewhere during the time under consideration.

• If N is the population density at time ‘t’, then its density at time ‘t+1’

Nt+1 = Nt + [(B + I) – (D + E)]

• Population density will increase if (B+I) > (D+E)

GROWTH MODELS

• EXPONENTIAL
• LOGISTIC

EXPONENTIAL GROWTH

•           When resources are unlimited, each species realizes its innate potential to grow in no. – population grows exponentially
•           N – Population size
b – Birth rates( per capita births)
d – Death rates (per capita deaths
dN/dt – increase/decrease in N during time t

Then,   dN/dt = (b – d)*N
Let (b – d) = r, then
dN/dt = r*N
Where, r – intrinsic rate of natural increase
For human population in 1981, r = 0.0205

Integral form of exponential growth eq.

                  Nt = N0ert

Where Nt = Population density after t
N0 =Initial population density
r   = Intrinsic rate of natural increase
e  = base of natural logarithms

•           Species growing exponentially under unlimited resources reaches enormous population density in short time.

LOGISTIC GROWTH
•           No population has unlimited resources-leads to competition for resources
•          Fittest individual survive and reproduce
•          Carrying capacity (K)- Maximum population density a habitat’s resources can support
•          When a population has limited resources it shows

1. lag phase
2. phase of acceleration
3. asympote- population density = K

Verhulst Pearl Logistic Growth

                          dN/dt = rN [(K – N)/K]

Where   N = Population density at time t
r = Intrinsic rate of natural increase
K = Carrying capacity

•           As resources for most organisms are finite logistic growth more realistic

LIFE HISTORY VARIATIONS

•          Darwinian fitness – Reproductive fitness
•          Organisms adopt most efficient reproductive strategy suited to their habitat

Examples:

1. Breed once in lifetime – pacific salmon fish ,Bamboo
2. Breed many times in life time – birds,  mammals
3. Produce large no. of small sized offspring  – Oysters, pelagic fishes
4. Produce small no. of large sized offspring – birds, mammals

Ecologists say life history traits depend on constraints of biotic and abiotic parts

 
Population Interactions

Minimum requirement of species- one more species to feed on.

Interspecific interactions – Interactions of populations of two different species.

Types of Interactions:

Name of Interaction        Species A       Species B

Mutualism                         +                   +
Competition                       –                    –
Predation                          +                   –
Parasitism                         +                   –
Commensalism                   +                   0
Ammensalism                     –                    0

+   Positive effect                    –  Detrimental effect                      0  Neutral effect 

PREDATION

It is an Interspecific Interaction where one animal kills and consumes the other weaker animal.

Roles of Predators

• Transfer energy from plants to higher trophic levels (position of organism in food chain)
• Control Prey population – Prickly pear cactus- moth
• Biological control of Agricultural pest
• Maintain species diversity by reducing intensity of competition among competing prey species

Q: Why predators are prudent?

A: Over exploitation of prey by the predators results in extinction of prey and predator.

Defense to lessen impact of predation

• Insects and frog – camouflage
• Monarch butterfly – poisonous

PLANTS MORPHOLOGICAL AND CHEMICAL DEFENCES

• Thorns- cactus and Acacia
• Produce and store chemical – Calotropis
• Nicotine, Caffeine, Quinin, Strychnine, opium – against grazers & browsers

COMPETITION
Interaction either among individuals of same species or between individuals of different species.

Occurs among closely related species but not always true

1. Unrelated species also compete- flamingo & fish compete for zooplankton
2. Feeding efficiency of a species reduce due to other species even if resources are plenty – Abingdon tortoise.

Evidence for competition
Competitive release – species distribution restricted to small areas due to competitively superior species.

GAUSE’S COMPETITION EXCLUSION PRINCIPLE
“Two closely related species competing for same resources cannot coexist as the competitively inferior one will be eliminated.”

Resource partition- Two competing species avoid competition by diff. feeding and foraging patterns-Mc Arthur (warblers foraging activities)

PARASITISM
It is the interaction where one species (parasite) depends on the other species (host) for food and shelter, host is harmed.

• Parasites and host self-evolve.
• Adaptations of parasites

– Loss of unnecessary sense organs
– Hooks and sucker
– Loss of digestive system
– High Reproductive capacity

• Parasites-

(i) Reduce the survival of host
(ii) Growth and reproductive rate are reduced
(iii) Render the host vulnerable to its predators by making them weak

Types of parasite

ECTOPARASITES–depend on external surface of host
Example – head lice on humans, ticks on dogs

ENDOPARASITES–take shelter within the body of the host organism
Example – Liverfluke, Plasmodium

MUTUALISM
It is interaction in which both the interacting species are benefited

Examples
1. Lichen – fungi and algae
2. Mycorrhizae – fungi and roots of higher plants
3. Pollination of plants by insects
4. Mediterranean orchid- sexual deceit for pollination- appears as female bee

AMENSALISM
Interaction between two different species, in which one species is harmed and the other species is neither harmed nor benefited. Example.  Bacterial culture, after few days fungus growth will be there on it like Pencillium, and its secretions of chemical will kill bacteria, but no benefits to fungi.