● `color{violet}("Populations")` evolve to maximise their `color{violet}("reproductive fitness")`, also called `color{brown}("Darwinian fitness")` `color{violet}("(high r value)")`, in the habitat in which they `color{violet}("live.")`

● Under a particular set of selection pressures, `color{violet}("organisms evolve")` towards the most efficient `color{brown}("reproductive strategy")`.

● Some `color{violet}("organisms breed")` only once in their `color{violet}("lifetime")` `color{brown}("(Pacific salmon fish, bamboo)")` while others breed many times during their `color{violet}("lifetime")` (most `color{brown}("birds")` and `color{brown}("mammals")`).

● Some produce a large number of small-sized `color{violet}("offspring")` (`color{brown}("Oysters, pelagic fishes")`) while others produce a small number of large-sized `color{violet}("offspring")` (`color{brown}("birds, mammals")`).

● `color{violet}("Ecologists")` suggest that life history `color{violet}("traits of organisms")` have evolved in relation to the constraints imposed by the `color{violet}("abiotic and biotic")` components of the habitat in which they live.

● `color{violet}("Evolution")` of life history `color{violet}("traits")` in different species is currently an important area of research being conducted by `color{violet}("ecologists.")`

● Can you think of any `color{violet}("natural habitat")` on earth that is `color{violet}("inhabited")` just by a single species.

● There is no such `color{violet}("habitat")` and such a situation is even `color{violet}("inconceivable.")`

● For any species, the `color{violet}("minimal requirement")` is one more species on which it can feed.

● Even a `color{violet}("plant")` species, which makes its own `color{violet}("food,")` cannot `color{violet}("survive")` alone; it needs `color{violet}("soil microbes")` to break down the `color{violet}("organic matter")` in `color{violet}("soil")` and return the `color{violet}("inorganic nutrients")` for `color{violet}("absorption.")`

● And then, the `color{violet}("plant")` cannot manage `color{violet}("pollination")` without an `color{violet}("animal agent.")`

● It is obvious that in nature, `color{violet}("animals, plants and microbes")` do not and cannot `color{violet}("live in isolation")` but interact in various ways to form a `color{brown}("biological community.")`

● Even in `color{violet}("minimal communities")`, many interactive linkages exist, although all may not be readily apparent.

● `color{brown}("Interspecific interactions")` arise from the `color{violet}("interaction")` of `color{violet}("populations")` of two different species.

● They could be `color{violet}("beneficial")`, detrimental or `color{violet}("neutral (neither harm nor benefit)")` to one of the species or both.

● Assigning a `‘+’` sign for `color{violet}("beneficial interaction")`, `‘-’` sign for detrimental and `‘0’` for `color{violet}("neutral interaction,")` we can look at all the possible outcomes of `color{violet}("interspecific interactions .")`

● Both the species benefit in `color{brown}("mutualism")` and both lose in `color{brown}("competition")` in their `color{violet}("interactions")` with each other.

● In both `color{brown}("parasitism")` and `color{brown}("Predation")` only one species `color{violet}("benefits (parasite and predator, respectively)")` and the interaction is detrimental to the other species `color{violet}("(host and prey, respectively)")`.

● The`color{violet}(" interaction")` where one species is `color{violet}("benefitted")` and the other is neither `color{violet}("benefitted")` nor `color{violet}("harmed")` is called `color{brown}("commensalism.")`

● In `color{brown}("amensalism")` on the other hand one species is `color{violet}("harmed")` whereas the other is `color{violet}("unaffected.")`

● `color{violet}("Predation, parasitism")` and `color{violet}("commensalisms")` share a common characteristic– the interacting species live closely together.

● One can think of `color{violet}("predation")` as `color{violet}("nature’s")` way of transferring to higher `color{violet}("trophic")` levels the energy fixed by `color{violet}("plants")`.

● When we think of `color{violet}("predator")` and `color{violet}("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 `color{violet}("animals eating plants")` are categorized separately as `color{brown}("herbivores,")` they are, in a broad `color{violet}("ecological")` context, not very different from `color{violet}("predators.")`

● Besides acting as `color{brown}("‘conduits’")` for energy transfer across `color{violet}("trophic levels")`, predators play other important roles.

● They keep `color{violet}("prey populations")` under control.

● But for `color{violet}("predators, prey")` species could achieve very high `color{violet}("population densities")` and cause `color{violet}("ecosystem instability.")`

● When certain exotic species are introduced into a `color{violet}("geographical area,")` they become invasive and start spreading fast because the `color{violet}("invaded land")` does not have its `color{violet}("natural predators.")`

● The `color{brown}("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 `color{violet}("under control")` only after a `color{violet}("cactus-feeding predator")` (a `color{brown}("moth")`) from its natural habitat was introduced into the country.



● `color{violet}("Biological control")` methods adopted in `color{violet}("agricultural pest control")` are based on the ability of the `color{violet}("predator")` to regulate `color{violet}("prey population.")`

● `color{violet}("Predators")` also help in maintaining species `color{violet}("diversity")` in a `color{violet}("community")`, by `color{violet}("reducing the intensity")` of competition among `color{violet}("competing prey")` species.

● In the `color{violet}("rocky intertidal communities")` of the American Pacific Coast the starfish `color{brown}("Pisaster")` is an important predator.

● In a field experiment, when all the starfish were removed from an enclosed `color{violet}("intertidal area,")` more than 10 species of invertebrates became extinct within a year, because of `color{violet}("interspecific competition")`.

● If a `color{violet}("predator")` is too `color{violet}("efficient")` and `color{violet}("overexploits")` its prey, then the prey might become extinct and following it, the `color{violet}("predator")` will also become extinct for lack of food.

● This is the reason why `color{violet}("predators")` in nature are `color{brown}("‘prudent’")`

● `color{violet}("Prey")` species have evolved various defenses to lessen the impact of `color{violet}("predation.")`

● Some species of insects and frogs are `color{brown}("cryptically-coloured (camouflaged)")` to avoid being detected easily by the `color{violet}("predator.")`



● Some are `color{violet}("poisonous")` and therefore avoided by the `color{violet}("predators.")`

● The `color{brown}("Monarch butterfly")` is highly distasteful to its `color{violet}("predator (bird)")` because of a special `color{violet}("chemical present")` in its body.

● `color{violet}("Interestingly")`, the `color{violet}("butterfly")` acquires this chemical during its caterpillar stage by feeding on a `color{violet}("poisonous weed.")`

● For plants, herbivores are the `color{violet}("predators.")`

● Nearly `25% `of all insects are known to be `color{brown}("phytophagous")` (feeding on plant sap and other parts of plants).

● The problem is particularly severe for `color{violet}("plants")` because, unlike `color{violet}("animals")`, they cannot run away from `color{violet}("their predators.")`

● `color{violet}("Plants")` therefore have evolved an `color{violet}("astonishing variety")` of `color{violet}("morphological and chemical")` defences against `color{violet}("herbivores.")`

● Thorns `color{brown}("(Acacia, Cactus)")` are the most common `color{violet}("morphological")` means of defence.

● `color{violet}("Many plants")` produce and store `color{violet}("chemicals")` that make the `color{violet}("herbivore")` sick when they are eaten, `color{violet}("inhibit feeding")` or `color{violet}("digestion")`, disrupt its reproduction or even kill it.

● There is a weed `color{brown}("Calotropis")` growing in abandoned fields.

● The `color{violet}("plant")` produces highly poisonous `color{brown}("cardiac glycosides")` and that is why we never see any cattle or goats browsing on this `color{violet}("plant")`.

● A wide variety of `color{violet}("chemical substances")` that we extract from `color{violet}("plants")` on a commercial scale (`color{violet}("nicotine, caffeine, quinine, strychnine, opium, etc.,")`) are produced by them actually as defences against grazers and browsers.