ORGANISM AND ITS ENVIRONMENT
Ecology at the organismic level is physiological ecology which defines how different organisms are adapted to their
environments in terms of not only survival but also reproduction.
Regional and local variations within each biome lead to the formation of a wide variety of habitats.
On planet Earth, along with few favourable habitats life exists in extreme and harsh habitats as well. For example the life at scorching desert,
rain-soaked forests, deep ocean trenches, torrential streams,
permafrost polar regions, high mountain tops, boiling thermal springs, etc.
Interestingly, our intestine is also an unique habitat for hundreds of species of microbes.
The key elements that lead to the variation in the physical
and chemical conditions of different habitats are:
a. Temperature,
b. Water,
c. Light and
d. Soil.
Major Abiotic Factors
a. Temperature
Temperature is the most ecologically relevant environmental factor.
The average temperature on land varies seasonally,
decreases progressively from the equator towards the poles and from plains to the mountain tops.
It ranges from subzero levels in polar areas and high altitudes to >50C in tropical deserts in summer.
It is general knowledge that mango trees do not and cannot grow in temperate countries like Canada and Germany,
snow leopards are not found in Kerala forests and tuna fish are rarely caught beyond tropical latitudes in the ocean.
A few organisms can tolerate and thrive in a wide range of temperatures (they are called eurythermal) but
majority of them are restricted to a narrow range of temperatures and such organisms are called stenothermal.
The levels of thermal tolerance of different species determine to a large extent their geographical distribution.
And in today's world there is a great concern regarding the increase in global temperature termed as global warming.
b. Water
Along with temperature, water is the most important factor influencing the life of organisms.
Life on earth was originated in water and is unsustainable without water.
The availability of water in desert is very low hence,
only special adaptations make it possible to live there.
The productivity and distribution of plants is also heavily dependent on water.
In general we think that organisms living in oceans, lakes and rivers must not have faced any water-related problems, but it is not true.
For aquatic organisms the quality (chemical composition, pH) of water becomes important.
The salt concentration (measured as salinity in parts per thousand), is less than
5 in inland waters, 30-35 in the sea and > 100 in some hypersaline lagoons.
Some organisms are tolerant of a wide range of salinities (euryhaline)
but others are restricted to a narrow range (stenohaline).
Many freshwater animals cannot live for long in sea water and vice versa
because of the osmotic problems, they face. c. Light
As plants produce food through photosynthesis, a process which is only possible when sunlight is available as a source of energy,
we can understand the importance of light for living organisms.
Many species of small plants (herbs and shrubs) growing in forests are adapted to photosynthesise
optimally under very low light conditions because they are constantly overshadowed by tall, canopied trees.
Many plants are also dependent on sunlight to meet their photoperiodic requirement for flowering.
For many animals also, light is important in a sense that they use the diurnal and seasonal variations in light
intensity and duration (photoperiod) as cues for timing their foraging, reproductive and migratory activities.
The availability of light on land is linked with temperature since the sun is the source for both.
But, deep (>500m) in the oceans, the environment is perpetually dark and
its inhabitants are not aware of the existence of a celestial source of energy called Sun.
The spectral quality of solar radiation is also very important for life.
The UV component of the spectrum is harmful to many organisms while not all the colour components of the visible spectrum
are available for marine plants living at different depths of the ocean.
d. Soil
The nature and properties of soil depends on the climate, the weathering process,
whether soil is transported or sedimentary and how soil development occurred.
Various characteristics of the soil like soil composition, grain size and aggregation
determine the percolation and water holding capacity of the soils.
These characteristics along with parameters such as pH, mineral composition
and topography determine to a large extent the vegetation in any area.
This in turn dictates the type of animals that can be supported.
Similarly, in the aquatic environment, the sediment-characteristics often
determine the type of benthic animals that can thrive there.
Responses to Abiotic Factors
During the course of millions of years of their existence, many species have evolved a relatively constant internal (within the body)
environment that permits all biochemical reactions and physiological functions to proceed with maximal efficiency
and thus, enhance the overall ‘fitness’ of the species.
Let us look at various possibilities way the other living organisms cope
(i) Regulate:
Some organisms are able to maintain homeostasis by physiological (sometimes behavioural also)
means which ensures constant body temperature, constant osmotic concentration, etc.
All birds and mammals, and a very few lower vertebrate and
invertebrate species are indeed capable of such regulation (thermoregulation and osmoregulation).
It is believed that the ‘success’ of mammals is largely due to their ability to maintain a constant body temperature
and thrive whether they live in Antarctica or in the Sahara desert.
The mechanisms used by most mammals to regulate their body temperature are similar to the ones that we humans use.
We maintain a constant body temperature of 37°C.
In summer, when outside temperature is more than our body temperature, we sweat profusely.
The resulting evaporative cooling, similar to what happens with a desert cooler in operation, brings down the body temperature.
In winter when the temperature is much lower than 37°C,
humans start to shiver, a kind of exercise which produces heat and raises the body temperature.
Whereas plants do not have such mechanisms to maintain internal temperatures.
(ii) Conform:
99 per cent of animals and nearly all plants cannot maintain a constant internal environment.
Their body temperature changes with the ambient temperature.
In aquatic animals,
the osmotic concentration of the body fluids change with that of the ambient water osmotic concentration.
These animals and plants are called conformers.
Heat loss or heat gain is a function of surface area.
Since small animals have a larger surface area relative to their volume,
they tend to lose body heat very fast when it is cold outside; then they have to expend much energy to generate body heat through metabolism.
This is the main reason why very small animals are rarely found in polar regions.
During the course of evolution, the costs and benefits of maintaining a constant internal
environment are taken into consideration.
Some species have evolved the ability to regulate, but only over a limited range of environmental conditions, beyond which they simply conform.
If the stressful external conditions are localised or remain only for a short duration, the organism has two other alternatives which are illustrated below:
(iii) Migrate:
The organism can move away temporarily from the stressful habitat to a more hospitable area and return when stressful period is over.
Many animals, particularly birds, during winter undertake long-distance migrations to more hospitable areas.
(iv) Suspend:
In bacteria, fungi and lower plants, various kinds of thickwalled
spores are formed which help them to survive unfavourable
conditions these germinate on availability of suitable environment.
In higher plants, seeds and some other vegetative reproductive structures serve
as means to tide over periods of stress besides helping in dispersal where they germinate to form new plants under favourable moisture and temperature conditions.
They are able to do so by reducing their metabolic activity and going into a state of ‘dormancy’.
Some snails and fish go into aestivation to avoid summer–related problems-heat and dessication.
Under unfavourable conditions many zooplankton species in lakes and ponds enter diapause, a stage of suspended development.
Adaptations
Definition & Introduction
Adaptation is any attribute of the organism (morphological, physiological, behavioural) that enables the organism to survive and reproduce in its habitat.
Many adaptations have evolved over a long evolutionary time and are genetically fixed.
In the absence of an external source of water,
the kangaroo rat in North American deserts is capable of meeting all its
water requirements through its internal fat oxidation (in which water is a by product).
It also has the ability to concentrate its urine so that
minimal volume of water is used to remove excretory products.
Many desert plants have a thick cuticle on their leaf surfaces and
have their stomata arranged in deep pits to minimise water loss through transpiration.
They also have a special photosynthetic pathway (CAM)
that enables their stomata to remain closed during day time.
Desert plants like Opuntia, have no leaves and they are reduced to spines–and the
photosynthetic function is taken over by the flattened stems.
Mammals from colder climates generally have shorter ears
and limbs to minimise heat loss and this is called the Allen’s Rule.
In the polar seas aquatic mammals like seals have a thick layer of fat (blubber) below their
skin that acts as an insulator and reduces loss of body heat.
Some organisms possess adaptations that are physiological which allow them to respond quickly to a stressful situation.
High altitude place (>3,500m ) people experience an altitude sickness.
Its symptoms include nausea, fatigue and heart palpitations.
This is because in the low atmospheric pressure of high altitudes, the body does not get enough oxygen.
But, gradually people get acclimatised and stop experiencing altitude sickness.
Reason behind it
The body compensates low oxygen availability by increasing red blood cell production, decreasing the binding affinity of hemoglobin and by increasing breathing rate.
In most animals, the metabolic reactions and hence all the physiological functions proceed optimally in a narrow temperature range (in humans, it is 37°C).
But there are microbes (archaebacteria) that flourish in hot springs and deep sea hydrothermal vents where temperatures far exceed 100°C.
Many fish thrive in Antarctic waters where the temperature is always below zero.
A large variety of marine invertebrates and fish live at great depths in the ocean where the pressure is >100 times the normal atmospheric pressure .
Organisms living in such extreme environments show a fascinating array of biochemical adaptations.
Some organisms show behavioural responses to cope with variations in their environment.
Desert lizards lack the physiological ability that mammals have to deal with the high temperatures of their habitat,
but manage to keep their body temperature fairly constant by behavioural means.
They bask in the sun and absorb heat when their body temperature drops below the comfort zone, but move into shade when the ambient temperature starts increasing.
Some species are capable of burrowing into the soil to hide and escape from the above-ground heat.
POPULATIONS
Population Attributes
A population has certain attributes that an individual organism does not.
An individual may have births and deaths, but a population has birth rates and death rates.
In a population these rates refer to per capita births and deaths, respectively.
The rates, hence, expressed is change in numbers (increase or decrease) with respect to members of the population.
For example
If in a pond there are 20 lotus plants last year and through reproduction 8 new plants are added,
taking the current population to 28, the birth rate is calculated as 8/20 = 0.4 offspring per lotus per year.
If 4 individuals in a laboratory population of 40 fruitflies died during a specified time interval,
the death rate in the population during that period is 4/40 = 0.1 individuals per fruitfly per week.
Another attribute characteristic of a population is sex ratio.
An individual is either a male or a female but a population has a sex ratio (e.g., 60 per cent of the population are females and 40 per cent males).
A population at any given time is composed of individuals of different ages.
If the age distribution (per cent individuals of a given age or age
group) is plotted for the population, the resulting structure is called an age pyramid as shown in figure below.
For human population, the age pyramids generally show age distribution of males and females in a combined diagram.
The shape of the pyramids reflects the growth status of the population :
(a) whether it is growing, (b) stable or (c) declining.
The size of the population defines its status in the habitat.
The size, in nature, could be as low as <10 or go into millions .
Population size, technically called population density (designated as N), need not necessarily be measured in numbers only.
Although total number is generally the most appropriate measure of population density,
it is in some cases either meaningless or difficult to determine.
In an area, if there are 200 Parthenium plants but only a single huge banyan tree with a large canopy,
stating that the population density of banyan is low relative to that of Parthenium amounts to underestimating the enormous role of the Banyan in that community.
In such cases, the per cent cover or biomass is a more meaningful measure of the population size.
Population Growth
The size of a population for any species is not a static parameter.
It keeps changing in time, depending on various factors including food availability, predation pressure and adverse weather.
The density of a population in a given habitat during a given period, fluctuates due to changes in four basic processes,
two of which (natality and immigration) contribute to an increase in population density and two (mortality and emigration) to a decrease.
(i) Natality refers to the number of births during a given period in the population that are added to the initial density.
(ii) Mortality is the number of deaths in the population during a given period.
(iii) Immigration is the number of individuals of the same species that
have come into the habitat from elsewhere during the time period under consideration.
(iv) Emigration is the number of individuals of the population who left the habitat and gone elsewhere during the time period under consideration.
So, if N is the population density at time t, then its density at time t +1 is Nt+1 = Nt + [(B + I) – (D + E)]
You can see from the above equation that population density will increase if the number of births plus the number of immigrants (B + I) is
more than the number of deaths plus the number of emigrants (D + E),
otherwise it will decrease. Under normal conditions, births and deaths are the most important factors influencing population density,
the other two factors assuming importance only under special conditions.
For instance, if a new habitat is just being colonised, immigration may contribute more significantly to population growth than birth rates.
Growth Models : Does the growth of a population with time show any specific and predictable pattern?
We have been concerned about unbridled human population growth and problems created by it in our country and it is therefore natural for us to be curious if different animal populations in nature behave the same way or show some restraints on growth.
Perhaps we can learn a lesson or two from nature on how to control population growth.
(i) Exponential growth: Resource (food and space) availability is obviously essential for the unimpeded growth of a population
Ideally, when resources in the habitat are unlimited, each species has the ability to realise fully its innate potential to grow in number,
as Darwin observed while developing his theory of natural selection.
Then the population grows in an exponential or geometric fashion. If in a population of size N, the birth rates (not total number but per capita births)
are represented as b and death rates (again, per capita death rates) as d,
then the increase or decrease in N during a unit time period t (dN/dt) will be
dN/dt = (b – d) × N
Let (b–d) = r, then
dN/dt = rN
The r in this equation is called the ‘intrinsic rate of natural
and is a very important parameter chosen for assessing impacts of any biotic or abiotic factor on population growth.
To give you some idea about the magnitude of r values, for the Norway rat the r is 0.015, and for the flour beetle it is 0.12.
In 1981, the r value for human population in India was 0.0205.
Find out what the current r value is. For calculating it, you need to know the birth rates and death rates.
The above equation describes the exponential or geometric growth pattern of a population (and results in a J-shaped curve when we plot N in relation to time.
If you are familiar with basic calculus, you can derive the integral form of the exponential growth equation as
Nt = N0ert where,
Nt = Population density after time t
N0 = Population density at time zero
r = intrinsic rate of natural increase
e = the base of natural logarithms
Any species growing exponentially under unlimited resource conditions can reach enormous population densities in a short time.
Darwin showed how even a slow growing animal like elephant could reach enormous numbers in the absence of checks.
The following is an anecdote popularly narrated to demonstrate dramatically how fast a huge
population could build up when growing exponentially.
(ii) Logistic growth: No population of any species in nature has at its
disposal unlimited resources to permit exponential growth.
This leads to competition between individuals for limited resources.
Eventually, the ‘fittest’ individual will survive and reproduce.
The governments of many countries have also realised this fact and introduced various restraints with a view to limit human population growth.
In nature, a given habitat has enough resources to support a maximum possible number, beyond which no further growth is possible.
Let us call this limit as nature’s carrying capacity (K) for that species in that habitat.
A population growing in a habitat with limited resources show initially a lag phase, followed by phases of acceleration
and deceleration and finally an asymptote, when the population density reaches the carrying capacity.
A plot of N in relation to time (t) results in a sigmoid curve.
This type of population growth is called Verhulst-Pearl Logistic Growth and is described by the following equation:
dN/dt = rN(K-N/k)
Where N = Population density at time t
r = Intrinsic rate of natural increase
K = Carrying capacity
Since resources for growth for most animal populations are finite and become limiting sooner or later, the logistic growth model is considered a more realistic one.
Life History Variation
Populations evolve to maximise their reproductive fitness, also called Darwinian fitness (high r value), in the habitat in which they live.
Under a particular set of selection pressures, organisms evolve towards the most efficient reproductive strategy. Some organisms breed only once in their lifetime (Pacific salmon fish, bamboo) while others breed many times during their lifetime (most birds and mammals).
Some produce a large number of small-sized offspring (Oysters, pelagic fishes) while others produce a small number of large-sized offspring (birds, mammals).
So, which is desirable for maximising fitness? Ecologists suggest that life history traits of organisms have evolved in relation to the constraints imposed by the abiotic and
biotic components of the habitat in which they live.
Evolution of life history traits in different species is currently an important area of research being conducted by ecologists.
Population Interactions
There is no such habitat and such a situation is even inconceivable.
For any species, the minimal requirement is one more species on which it can feed. Even a plant species, which makes its own food, cannot survive alone;
it needs soil microbes to break down the organic matter in soil and return the inorganic nutrients for absorption.
It is obvious that in nature, animals, plants and microbes do not and cannot live in isolation but interact in various ways to form a biological community.
Even in minimal communities, many interactive linkages exist, although all may not be readily apparent.
Interspecific interactions arise from the interaction of populations of two different species.
They could be beneficial, detrimental or neutral (neither harm nor benefit) to one of the species or both.
Assigning a ‘+’ sign for beneficial interaction, ‘-’ sign for detrimental and 0 for neutral interaction,
Both the species benefit in mutualism and both lose in competition in their interactions with each other. In both parasitism and predation only
one species benefits (parasite and predator, respectively) and the interaction is detrimental to the other species (host and prey, respectively).
The interaction where one species is benefitted and the other is neither benefitted nor harmed is called commensalism.
In amensalism on the other hand one species is harmed whereas the other is unaffected.
Predation, parasitism and commensalism share a common characteristic– the interacting species live closely together.
(i) Predation: When we think of predator and prey, most probably it is the tiger and the deer that readily come to our mind, but a sparrow eating any seed is no less a predator.
Although animals eating plants are categorised separately as herbivores, they are, in a broad ecological context, not very different from predators.
Besides acting as ‘conduits’ for energy transfer across trophic levels, predators play other important roles.
They keep prey populations under control.
But for predators, prey species could achieve very high population densities and cause ecosystem instability.
When certain exotic species are introduced into a geographical area, they become invasive and start spreading fast because the invaded land does not have its natural predators.
The prickly pear cactus introduced into Australia in the early 1920’s caused havoc by spreading rapidly into millions of hectares of
rangeland. Finally, the invasive cactus was brought under control only after a cactus-feeding predator (a moth) from its natural habitat was introduced into the country. Biological control methods adopted
in agricultural pest control are based on the ability of the predator to regulate prey population.
Predators also help in maintaining species diversity in a community, by reducing the intensity of competition among competing prey species. In the rocky intertidal communities of the American Pacific Coast the starfish Pisaster is an important predator.
In a field experiment, when all the starfish were removed from an enclosed intertidal area, more than 10 species of invertebrates became extinct within a year, because of interspecific competition.
If a predator is too efficient and overexploits its prey, then the prey might become extinct and following it,
the predator will also become extinct for lack of food. This is the reason why predators in nature are ‘prudent’.
Prey species have evolved various defenses to lessen the impact of predation.
Some species of insects and frogs are cryptically-coloured (camouflaged) to avoid being detected easily by the predator. Some are poisonous and therefore avoided by the predators.
The Monarch butterfly is highly distasteful to its predator (bird) because of a special chemical present in its body.
Interestingly, the butterfly acquires this chemical during its caterpillar stage by feeding on a poisonous weed.
For plants, herbivores are the predators. Nearly 25 per cent of all insects are known to be phytophagous (feeding on plant sap
and other parts of plants). The problem is particularly severe for plants because, unlike animals, they cannot run away from their predators. Plants therefore have evolved an astonishing variety of morphological and chemical defences against herbivores.
Thorns (Acacia, Cactus) are the most common morphological means of defence.
Many plants produce and store chemicals that make the herbivore sick when they are eaten, inhibit feeding or digestion, disrupt its reproduction or even kill it.
. The plant produces highly poisonous cardiac glycosides and that is why you never see any cattle or goats browsing on this plant.
A wide variety of chemical substances that we extract from plants on a commercial scale (nicotine, caffeine, quinine, strychnine, opium, etc.,) are produced by them actually as defences against grazers and browsers.
(ii) Competition:
When Darwin spoke of the struggle for existence and survival of the fittest in nature, he was convinced that interspecific competition is a potent force in organic evolution.
It is generally believed that competition occurs when closely related species compete for the same resources that are limiting, but this is not entirely true.
Firstly, totally unrelated species could also compete for the same resource.
For instance, in some shallow South American lakes visiting flamingoes and resident fishes compete for their common food, the zooplankton in the lake.
Secondly, resources need not be limiting for competition to occur; in interference competition, the feeding efficiency of one species might be reduced due to the interfering and inhibitory presence of the other species, even if resources (food and space) are abundant.
Therefore, competition is best defined as a process in which the fitness of one species (measured in terms of its ‘r’ the intrinsic rate of increase) is significantly lower in the presence of another species.
It is relatively easy to demonstrate in laboratory experiments, as Gause and other experimental ecologists did, when resources are
limited the competitively superior species will eventually eliminate the other species,
but evidence for such competitive exclusion occurring in nature is not always conclusive.
Strong and persuasive circumstantial evidence does exist however in some cases.
The Abingdon tortoise in Galapagos Islands became extinct within a decade after goats were introduced on the island, apparently due to the greater browsing efficiency of the goats.
Another evidence for the occurrence of competition in nature comes from what is called ‘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 experiments showed that on the rocky sea coasts of Scotland, the larger and competitively superior barnacle Balanus dominates the intertidal area,
and excludes the smaller barnacle Chathamalus from that zone.
In general, herbivores and plants appear to be more adversely affected by competition than carnivores.
Gause’s ‘Competitive Exclusion Principle’ states that two closely related species competing for the same resources cannot
co-exist indefinitely and the competitively inferior one will be eliminated eventually. This may be true if resources are limiting,
but not otherwise. More recent studies do not support such gross generalisations about competition.
While they do not rule out the occurrence of interspecific competition in nature,
they point out that species facing competition might evolve mechanisms that promote co-existence rather than exclusion. One such mechanism is ‘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 patterns. MacArthur showed that five closely related species of warblers living on the
same tree were able to avoid competition and co-exist due to behavioural differences in their foraging activities.
g (iii) Parasitism:
Considering that the parasitic mode of life ensures free lodging and meals, it is not surprising that parasitism has evolved in so many taxonomic groups from plants to higher vertebrates.
Many parasites have evolved to be host-specific (they can parasitise only a single species of host) in such a way that both host and the parasite tend to co-evolve;
that is, if the host evolves special mechanisms for rejecting or resisting the parasite, the parasite has to evolve mechanisms to counteract and neutralise them, in order to be successful with the same host species.
9In accordance with their life styles, parasites evolved special adaptations such as the loss of unnecessary sense organs,/
, presence of adhesive organs or suckers to cling on to the host, loss of digestive system and high reproductive capacity. ;.
The life cycles of parasites are often complex, involving one or two intermediate hosts or vectors to facilitate parasitisation of its primary host.
The human liver fluke (a trematode parasite) depends on two intermediate hosts (a snail and a fish) to complete its life cycle.
The malarial parasite needs a vector (mosquito) to spread to other hosts. Majority of the parasites harm the host; they may reduce the survival, growth and reproduction of the host and reduce its population density.
They might render the host more vulnerable to predation by making it physically weak.
Parasites that feed on the external surface of the host organism are called ectoparasites.
The most familiar examples of this group are the lice on humans and ticks on dogs.
Many marine fish are infested with ectoparasitic copepods. Cuscuta, a parasitic plant that is commonly found growing on hedge plants, has lost its chlorophyll and leaves in the course of evolution.
It derives its nutrition from the host plant which it parasitises. The female mosquito is not considered a parasite, although it needs our blood for reproduction.
In contrast, endoparasites are those that live inside the host body at different sites (liver, kidney, lungs, red blood cells, etc.).
The life cycles of endoparasites are more complex because of their extreme specialisation.
Their morphological and anatomical features are greatly simplified while emphasising their reproductive potential.
Brood parasitism in birds is a fascinating example of parasitism in which the parasitic bird lays its eggs in the nest of its host
and lets the host incubate them. During the course of evolution, the eggs of the parasitic bird have evolved to resemble the host’s egg in
size and colour to reduce the chances of the host bird detecting the foreign eggs and ejecting them from the nest.
on (spring to summer) and watch brood parasitism in action.
(iv) Commensalism:
This is the interaction in which one species benefits and the other is neither harmed nor benefited.
An orchid growing as an epiphyte on a mango branch, and barnacles growing on the back of a whale benefit while neither the mango tree nor the whale derives any apparent benefit.
The cattle egret and grazing cattle in close association, a sight you are most likely to catch if you live in farmed rural areas, is a classic example of commensalism.
The egrets always forage close to where the cattle are grazing because the cattle,
as they move, stir up and flush out from the vegetation insects that otherwise might be difficult for the egrets to find and catch.
Another example of commensalism is the interaction between sea anemone that has stinging tentacles and the clown fish that lives among them.
The fish gets protection from predators which stay away from the stinging tentacles.
The anemone does not appear to derive any benefit by hosting the clown fish.
(v) Mutualism:
This interaction confers benefits on both the interacting species. Lichens represent an intimate mutualistic relationship between a fungus and photosynthesising algae or cyanobacteria.
Similarly, the mycorrhizae are associations between fungi and the roots of higher plants.
The fungi help the plant in the absorption of essential nutrients from the soil while the plant in turn provides the fungi with energy-yielding carbohydrates.
The most spectacular and evolutionarily fascinating examples of mutualism are found in plant-animal relationships.
Plants need the help of animals for pollinating their flowers and dispersing their seeds.
Animals obviously have to be paid ‘fees’ for the services that plants expect from them.
Plants offer rewards or fees in the form of pollen and nectar for pollinators and juicy and nutritious fruits for seed dispersers.
But the mutually beneficial system should also be safeguarded against ‘cheaters’, for example, animals that try to steal nectar without aiding in pollination.
. It means that a given fig species can be pollinated only by its ‘partner’ wasp species and no other species.
The female wasp uses the fruit not only as an oviposition (egg-laying) site but uses the developing seeds within the fruit for nourishing its larvae.
The wasp pollinates the fig inflorescence while searching for suitable egg-laying sites.
In return for the favour of pollination the fig offers the wasp some of its developing seeds, as food for the developing wasp larvae.
Orchids show a bewildering diversity of floral patterns many of which have evolved to attract the right
pollinator insect (bees and bumblebees) and ensure guaranteed pollination by it .
Not all orchids offer rewards. The Mediterranean orchid Ophrys employs ‘sexual deceit’ to get pollination done by a species of bee.
One petal of its flower bears an uncanny resemblance to the female of the bee in size, colour and markings.
The male bee is attracted to what it perceives as a female, ‘pseudocopulates’ with the flower, and during that process is dusted with pollen from the flower.
When this same bee ‘pseudocopulates’ with another flower, it transfers pollen to it and thus, pollinates the flower.
. If the female bee’s colour patterns change even slightly for any reason during evolution, pollination success will be reduced unless the orchid flower co-evolves to maintain the resemblance of its petal to the female bee.
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