ORGANISMS AND POPULATIONS

ORGANISMS AND POPULATIONS

 

ORGANISM AND ITS ENVIRONMENT:

·         Rotation of sun and the tilt of its axis cause annual variations in the intensity and duration of temperature, resulting distinct seasons.

·         These variations along with annual variations in precipitation, forms major biomes, such as desert, rain forest, and tundra.

·         Temperature, water, light and soil are the key elements that lead to so much variation in the physical and chemical conditions of habitats.

·         Both abiotic (physic-chemical) and biotic components (pathogen, parasites, predators, competitions) characterize the habitat of an organism.

Major abiotic factors:

Temperature:

·         Temperature decreases progressively from equator towards the pole and high altitudes to > 50^o C in tropical deserts in summer.

·         Thermal springs and deep-sea hydrothermal vents are unique with >100^o C.

·         Temperature affects the kinetics of enzymes, BMR and other physiological actions.

·         Eurythermals: organism which can tolerate wide range of temperatures.

·         Stenothermal: organism which can tolerate narrow range of temperatures.

 

Water:

·         Water is also important factor that influence the life of organism.

·         The productivity and distribution of plants is also depends on water.

·         The salinity varies in aquatic environment:

o    5% in inland waters (fresh water)

o    30-35 in sea water

o    More than 100percent in hyper saline lagoons.

 

·         Euryhaline: organism which can tolerate wide range of salinity

·         Stenohaline: organism which can tolerate narrow range of salinity.

Light:

·         Plant produce food by photosynthesis, which only possible in presence of light. Hence it very important for autotrophs.

·         Plant species (herbs and shrubs) adapted for photosynthesize under canopy

·         Sunlight is required for photoperiodic response like flowering.

·         Animals use diurnal and seasonal variations in light intensity and photoperiod as cues for timing their foraging, reproductive and migration.

Soil:

·         Properties of soil vary according to the climate, the weathering process.

·         Soil composition, grain size and aggregation determine the percolation and water holding capacity of the soil.

·         These characteristic along with pH, mineral composition and topography determine to a large extent the vegetation in any area.

·         The sediment-characteristic often determine the type of benthic animal in aquatic environment.

Response to Abiotic Factors:

·         Homeostasis; the process by which the organism maintain a constant internal environment in respect to changing external environment.

How does organism cope with the changing environment?

Regulate:

·         Some organisms are able to maintain homeostasis physiological (sometimes behavioral also) means which ensures constant body temperature, constant osmotic concentration.

·         All birds and mammals and few lower invertebrates are capable of such regulation i.e. thermoregulation and osmoregulation.

·         Success of mammals is due to thermoregulation.

·         We maintain a constant body temperature of 37^oC.

·         When outside temperature is high we sweat profusely and evaporative cooling take place to bring body temperature down.

·         In winter due to low temperature outside our body temperature falls below 37^oC, we start to shiver, to generate heat to raise body temperature.

Conform: (i) Majority (99%) of animals and plants cannot maintain a constant internal environment; their body temperature varies according to ambient temperature.

·         In aquatic animals the osmotic concentration of body fluid varies with ambient water osmotic concentration.

·         All the above animals and plants are simply called as conformer.

Why the conformer not evolved to became regulators?

·         Thermoregulation is energetically expensive for many animals.

·         Small animal like shrews and humming birds cannot afford so much energy for thermoregulation.

·         Heat loss or heat gain is a function of surface area.

·         Small animals have larger surface area relative to their volume, they tend to lose body heat very fast when it is cold outside; then has to expend much energy to generate body heat through metabolism.

·         This is why very small animals are rarely found in Polar Regions.

Alternative response for stressful conditions is localized or remains for short duration.

 

Migrate:

• The organism moved away temporarily from the stressful habitat to a more hospitable area and return when stressful condition is over.
• Bird migrate form the colder region to warmer region.

Suspend:

• Thick walled spores are formed in microbes to overcome unfavourable stressful external environment. Spores germinate in favourable condition.
• In higher plants seeds and other vegetative reproductive structures are means to tide over the stress. They reduce their metabolic activity and going into a state of ‘dormancy’.
• Hibernation: during winter animals like bears escape in time
• Aestivation: animals like snail and fish avoid summer related problem like heat and desiccation.
• Diapauses: many zooplanktons undergo a stage of suspended development in unfavourable conditions.

ADAPTATION:

• Adaptation: is any attribute of the organism (morphological, physiological, and behavioral) that enables the organism to survive and reproduce in its habitat.

Adaptation of animal in desert:

• Kangaroo rat meets their water requirement from oxidation of fat.
• Excrete very concentrate urine to conserve water.

Adaptation of plant in desert (xerophytes)

• Thick cuticle on their leaf surfaces.
• Sunken stomata, both to reduce transpiration.
• Have special photosynthetic pathway (CAM), stomata closed during day time and remained open during night.
• Opuntia has no leaf- they are reduced to spines.
• Photosynthesis takes place in flat green stems.

Adaptation of animal in cold climate:

• Allen’s Rule: mammals from colder climates generally have shorter ears and limbs to minimize heat loss.
• Seals of polar aquatic seas have a thick layer of fat called blubber below their skin that acts as insulator and reduces loss of body heat.

Adaptation in high altitude:

• A person move to high altitude (>3,500 meter), develop altitude sickness.
• Symptoms developed are nausea, fatigue and heart palpitations.
• This is due to low atmospheric pressure of high altitudes; the body does not get enough oxygen.

How the bodies solve the problem?

• The body compensates low oxygen availability by increasing red blood cell production.
• The body compensates decreasing binding capacity of hemoglobin with oxygen by increasing rate of breathing.

Behavioral adaptation:

• Desert lizards are conformer hence they cope with the stressful environment by behavioral adaptations:
• They bask in the sun and absorb heat when their body temperature drops below the comfort zone in winter.
• Move to shade when the ambient temperature starts increasing.
• Some species burrowing into the soil to hide and escape from the above-ground heat.

POPULATION:

Population attributes:

• Population: a group of individual living in a well defined geographical area, share or compete for similar resources, potentially interbreed.
• Birth rate and death rate refers to per capita births and deaths respectively.
• Another attribute is sex ratio. The ratio between male female in a population.
• If the age distribution is plotted for a population the resulting structure is called age pyramid.
• The shape of the pyramids reflects the growth status of the population like growing, stable or declining.
• The population size is more technically called as population density.

Methods for measurement of population density:

·         Counting the number

·         Percent cover

·         Biomass.

·         Pug marks and fecal pellets for tiger census

Population growth:

• The size of the population changes depending on food availability, predation pressure and reduce weather.
• Population size fluctuated due to changes in four basic processes, two of which (Natality and immigration) contribute an increase in population density and two (mortality and emigration) to a decrease.
• Natality: number of birth in given period in the population.
• Mortality: number of deaths in the population in a given period of time.
• Immigration: is the number of individuals of same species that have come into the habitat from elsewhere during a given period of time.
• Emigration: number of individuals of the population who left the habitat and gone elsewhere during a given time period.
•   If  ‘N’  is  the  population  density  at  time  ‘t’,  then  its  density  at  time  t  +  1  is  :

Where B = the number of births
I = the number of immigrants
D = the number of deaths
E = the number of Emigrants.
N = Population Density
r = Intrinsic rate of natural increase
t = Time period
K  =  Carrying  capacity  (The  maximum  population  size  that  an  environment  can  sustain)

Exponential growth:

• The Exponential growth equation is  N_t = N₀e^rt
• Nt  =  Population  density  after  time  t
• N0  =  Population  density  at  time  zero
• r  =  intrinsic  rate  of  natural  increase
• e  =  the  base  of  natural  logarithms  (2.71828)

Exponential growth (‘J’ shape curve is obtained).
*    When resources are not limiting the growth.
*   Any  species  growth  exponentially  under  unlimited  resources  conditions  can  reach enormous  population  densities  in  a  short  time.
*    Growth is not so realistic.
Logistic growth model

• Verhulst-Pearl  Logistic  Growth  is  described  by  the  following  equations 
• dN/dt  =  rN  (K–N  /  N)
• Where  N  =  Population  density  at  time  t
• r  =  Intrinsic  rate  of  natural  increase
• K  =  Carrying  capacity

Logistic Growth (Sigmoid curve is obtained)

• When responses are limiting the Growth.
• Resources  for  growth  for  most  animal  populations  are  finite  and  become  limiting.
• The logistic growth model is a more realistic one.

POPULATION INTERACTIONS:

Predation:

• Organism of higher trophic level (predator) feeds on organism of lower trophic level (prey) is called the predation.
• Even the herbivores are not very different from predator.
• Predator acts as a passage for transfer of energy across trophic level.
• Predators keep prey populations under control.
• Exotic species have no natural predator hence they grow very rapidly. (prickly pear cactus introduced in Australia created problem)
• Predators also help in maintaining species diversity in a community, by reducing the intensity of competition among competing prey species. (Pisaster starfish field experiment)

Defense developed by prey against predators:

Animals:

• Insects and frogs are cryptically coloured (camouflaged) to avoid being detected by the predator.
• Some are poisonous and therefore avoided by the predators.
• Monarch butterfly is highly distasteful to its predator (bird) due to presence of special chemical it its body. The chemical acquired by feeding a poisonous weed during caterpillar stage.

Plants:

• Thorns in Acacia, Cactus are morphological means of defense.
• Many plants produce and store some chemical which make the herbivore sick if eaten, inhibit feeding, digestion disrupt reproduction, even kill the predators.
• Calotropis produces poisonous cardiac glycosides against herbivores.
•  Nicotine, caffeine, quinine, strychnine, opium etc. are produced by plant actually as defenses against the grazers and browsers.

 

Competition:

• Interspecific competition is a potent force in organic evolution.
• Competition generally occurs when closely related species compete for the same resources that are limiting, but this not entirely true:
• Firstly: totally unrelated species could also compete for the same resources.
• American lakes visiting flamingoes and resident fishes have their common food, zooplanktons.

 

• Secondly: resources need not be limiting for competition to occur.
• Abingdon tortoise in Galapagos Islands became extinct within a decade after goats were introduced on the island, due to greater browsing ability.

 

• Competitive release: A species, whose distribution is restricted to a small geographical area because of the presence of a competitively superior species, is found to expand its distributional range dramatically when the competing species is experimentally removed.
• Connell’s elegant field experiment showed that superior barnacle Balanus dominates the intertidal area and excludes the smaller barnacle Chathamalus from that zone.

 

• Gause’s ‘competitive Exclusion Principle’: two closely related species competing for the same resources cannot co-exist indefinitely and the competitively inferior will be eliminated eventually.
• Resource partitioning: If two species compete for the same resource, they could avoid competition by choosing, for instance, different times for feeding or different foraging pattern.
• MacArthur showed five closely related species of warblers living on the same tree were able to avoid competition and co-exist due to behavioral differences in their foraging activities.

Parasitism:

• Parasitic mode of life ensures free lodging and meals.
• Some parasites are host-specific (one parasite has a single host) in such a way that both host and parasite tend to co-evolve.

Parasitic adaptation

• Loss of unnecessary sense organs.
• Presence of adhesive organs or suckers to cling on to the host.
• Loss of digestive system.
• High reproductive capacity
• Parasites having one or more intermediate host or vectors to facilitate parasitisation of its primary host.
• Liver fluke has two intermediate hosts (snail and a fish) to complete its live cycle.

 Effects on the host:

• Parasite always harms the host.
• They reduce the survival, growth and reproduction of the host.
• Reduce its population density.
• They make the host more vulnerable to the predators, by making it physically weak.

 

•  Ectoparasite: feeds on the external surface of the host.
• Lice on human
• Ticks on dog
• Marine fish infested with copepods
• Cuscutaa parasitic plant grow on hedge plants.

 

• Endoparasites: are those that live inside the host body at different sites.
• Life cycle is more complex.
• Morphological and anatomical features are greatly simplified.
• Highly developed reproductive system.

 

• Brood parasitism:
• Special type of parasitism found in birds.
• The parasitic birds lay its eggs in the nest of its host and let the host incubate them.
• The egg of the host is very similar with the egg of the host.
• Cuckoo lays eggs in the nest of the crow.

Commensalism: This is the interaction in which one species benefits and the other is neither benefited nor harmed.

• Orchids growing as an epiphyte on a mango branch.
• Clown fish living among tentacles of sea anemone.
• Barnacles on back of whales.
• Cattle Egret and grazing cattle.

Mutualism: interaction between two living organism, both are equally benefited, no one is harmed.

• Lichen: a mycobiont and a Phycobiont.
• Mycorrhiza: relationship between fungi and root of higher plant.
• Pollinating insects and flowering plants.
• Fig trees and its pollinating agent wasp.

Sexual deceit

• Mediterranean orchid Ophrys employs ‘sexual deceit’.
• Petal of the flower resembles the female bee.
• The male bee attracted to what it perceives as a female, ‘pseudocopulates’ with the flower but does not get any benefits.