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Organisms and Populations - Population Interactions (Mutualism, Competition, Predation, Parasitism)

Grade 12CBSEBiology

Review the key concepts, formulae, and examples before starting your quiz.

🔑Concepts

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Interspecific interactions arise from the interaction of populations of two different species. These interactions can be classified as Beneficial (+), Detrimental (-), or Neutral (0).

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Predation (+/-): The predator benefits while the prey is harmed. Predators act as 'conduits' for energy transfer across trophic levels and maintain species diversity by reducing competition among prey species.

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Competition (-/-): Occurs when two species vie for the same limiting resources. According to Gause’s Competitive Exclusion Principle, two closely related species competing for the same resources cannot co-exist indefinitely and the competitively inferior one will be eliminated eventually.

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Resource Partitioning: If two species compete for the same resource, they could avoid competition by choosing different times for feeding or different foraging patterns (e.g., MacArthur's Warblers).

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Parasitism (+/-): The parasite derives nutrition from the host. Parasites can be Ectoparasites (e.g., ticks on dogs, CuscutaCuscuta on hedge plants) or Endoparasites (e.g., PlasmodiumPlasmodium in RBCs). Brood parasitism is seen in birds like the Cuckoo (KoelKoel).

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Mutualism (+/+): Both species benefit. Examples include Lichens (Algae + Fungi), Mycorrhizae (Fungi + Roots of higher plants), and the relationship between Fig trees and Wasp pollinators.

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Commensalism (+/0): One species benefits and the other is neither harmed nor benefited. Example: An Orchid growing as an epiphyte on a mango branch or Barnacles growing on the back of a whale.

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Amensalism (-/0): One species is harmed whereas the other is unaffected. For example, the secretion of chemicals by PenicilliumPenicillium that inhibits the growth of bacteria.

📐Formulae

Exponential Growth: dNdt=rN\text{Exponential Growth: } \frac{dN}{dt} = rN

Logistic Growth (Verhulst-Pearl): dNdt=rN(K−NK)\text{Logistic Growth (Verhulst-Pearl): } \frac{dN}{dt} = rN \left( \frac{K - N}{K} \right)

Intrinsic Rate of Natural Increase: r=(b−d)\text{Intrinsic Rate of Natural Increase: } r = (b - d)

💡Examples

Problem 1:

Explain the interaction where the Mediterranean orchid OphrysOphrys employs 'sexual deceit' for pollination.

Solution:

Mutualism (specifically specialized co-evolution).

Explanation:

The orchid OphrysOphrys has one petal that resembles the female of a bee species in size, color, and markings. The male bee is attracted to it and 'pseudocopulates' with the flower. During this process, pollen is dusted on the bee. When the bee repeats this with another flower, pollination occurs. If the female bee's color pattern changes slightly during evolution, the orchid must also co-evolve its petal pattern to maintain the 1:11:1 pollination success.

Problem 2:

In a rocky intertidal community of the American Pacific Coast, the starfish PisasterPisaster is an important predator. If all starfish are removed from an enclosed area, more than 1010 species of invertebrates become extinct within a year. Why?

Solution:

Interspecific Competition.

Explanation:

The predator (PisasterPisaster) helps in maintaining species diversity by reducing the intensity of competition among various prey species. In its absence, the most dominant prey species outcompete the others, leading to their extinction.

Problem 3:

A population of NN individuals shows a growth rate where r=0.05r = 0.05 and K=1000K = 1000. Calculate the rate of change dNdt\frac{dN}{dt} when N=500N = 500.

Solution:

dNdt=12.5 individuals per unit time\frac{dN}{dt} = 12.5 \text{ individuals per unit time}

Explanation:

Using the formula dNdt=rN(K−NK)\frac{dN}{dt} = rN \left( \frac{K - N}{K} \right), substitute the values: dNdt=0.05×500×(1000−5001000)=25×(5001000)=25×0.5=12.5\frac{dN}{dt} = 0.05 \times 500 \times \left( \frac{1000 - 500}{1000} \right) = 25 \times \left( \frac{500}{1000} \right) = 25 \times 0.5 = 12.5.

Population Interactions (Mutualism, Competition, Predation, Parasitism) Revision - Class 12…