Population Interactions | Biology Class 12 - NEET PDF Download

Inter-Specific Interactions

Due to increase in different species in community, interaction (for food, habitat) also starts between them.

Interspecific Interactions

(a) Positive or beneficial interaction – Member of one or both the interacting species are benefitted but neither is harmed.

(b) Negative interaction – One or both interacting species is harmed.  

Positive or Negative Interactions

It is a wide spread phenomenon, it includes → mutualism, commensalism, protocooperation.

1. Mutualism (+/+) or Symbiosis

Positive inter specific interaction in which members of two different species completely depend on each other for growth and survival, physical contact is present in between both the interacting species. It is obligatory relationship.

• Mutualism between animal and animal– e.g.Termites and Flagellates (Trichonympha).

• Mutualism between plant & animals – e.g. Yucca plant flowers and Pronuba insects – Pollination of yucca plant by pronuba (Female yucca moth).

• Mutualism between plant and bacteria – e.g. legume plant and Rhizobium.

• Mutualism between algae and higher plant – e.g. Nostoc, Anabaena and Anthoceros plant.

• Mutualism between algae and fungi– e.g. Lichens.

• Mutualism between fungi and higher plants– e.g. Mycorrhizal association.

Examples:

• Fig tree and wasp species:

In many species of fig trees, there is a tight one to one relationship with the pollinator species of wasp. 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 with in the fruit for nourishing its larval. 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.

Fig and Wasp

• Bees and orchid flower;

Orchids show diversity of floral patterns, which have evolved to attract the right pollinator insect (bees and bumblebees) and ensure guaranteed pollination by it.
The mediterranean orchid Ophrys employs "sexual deceit" to get pollination done by a species of bee. One petal of its flower beans resemble 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, it transfers pollen to it and thus, pollinates the flower.

2. Commensalism (+ / 0) 

Association between members of two species in which one is benefitted while other is almost unaffected.

• Lianas – are woody plants. Their roots are present in soil but their stem use other plant or object for support to get better light. They are found in dense forest. No nutritional relationship.  Lianas are the speciality of tropical rain forest. e.g. Bauhinia, Tinospora.

• Epiphytes – Small plants grow on other plants in tropical rain forest. They utilise only the space of host plant for light & humidity e.g. Orchids, Hanging mosses.

• Epizones – Those animals which depends on plants or other animals.
  Sucker fish (Echeneis) – Shark
  Pilot fish – Shark
  E.coli bacteria – Intestine of man
  Clown fish – Sea anemone
  Barnacles – Whale
  Cattle egret birds – Cattle

3. Proto-Cooperation (+/+)

Association in which both organisms are benefited but can live separately, it is a facultative or optional or occasional association also called as non-obligatory relationship. e.g.

• Hermit crab – Sea anemone

• Tick bird (Red-billed or yellow billed) – Rhinoceros

• Crocodile – Bird

Negative Interaction (Antagonism/Detrimental)

Two types of negative interaction: 

1. Exploitation 

One species harms the other by making its direct or indirect use of support, shelter or food.

It is of two types: 

(a) Parasitism (+ / –)

This association involves individuals of two species of different size in which smaller (Parasite) is benefitted and larger (host) is harmed. The parasite gets nourishment and shelter from host but does not kill the host.

Type of Parasites

(i) Ectoparasite →  lives on the body of host.

•  Ectozooparasite – Leech on cattle, ticks on dogs, copepods on marine fish and lice, mosquitoes, sandfly live on man

•  Ectophytoparasite – Amphids, Lac insects, Red cotton bug.

(ii) Endoparasites → lives in the body of host.

•  Tapeworm, Taenia, Ascaris, Entamoeba → live in intestine of man.

•  Plasmodium → live in R.B.C. of human.

(b) Predation (+/–)

A free living organisms which catches and kills another species for food.

Insectivores fungi – Dactylella, Dactylaria, Arthrobotrys.

Carnivores animals – Lion, snake.

Insectivores plants – Drosera, Utricularia, Nepenthes.

2. Amensalism (– / 0) 

In this interaction one species is inhibited by toxic secretion of another species. Inhibitor species is neither benefitted nor harmed.

Old NCERT Syllabus

Type of Amensalism

(i) Antibiosis – Secretion of antibiotics:

• Penicillium fungi secretes penicillin which inhibits growth of Staphylococcus bacteria.

• Chlorella algae secretes bacteriocytes which not only kills but also inhibits growth of the bacteria.

• Microcystis (BGA) secretes hydroxyl  amine, this causes the death of fishes.

(ii) Allelopathy – Secretion of toxic chemical:

• Parthenium – Trans Cinnamic acid is secreted by Parthenium which inhibits the growth of some plants like Cassia tora and Vincaregia. This phenomenon is known as allelopathy.

• Sunflower, Barley, Sorghum, Occimum also show allelopathy.

RAUNKIAER'S LIFE FORMS

On the basis of position and the degree of protection to perennating organs (bud) during adverse season, Raunkiaer divided the plant in to five life forms (growth process)

1. Phanerophytes – The buds are located much above the surface of the earth.

Such type of plants are found more in tropics, epiphytes are included in phanerophytes.

2. Chamaeophytes – The buds are situated very close/near to the ground surface. Such types of plants are found in cold places or high altitudes.

3. Hemicryptophytes – The buds present just below or just above the surface of ground. Such plants are found in temperate climate.

4. Cryptophytes – The buds lie very deep in the ground.

5. Therophytes – Those plants which are passing the unfavourable climate through their seeds.

SOME TERMINOLOGY RELATED TO COMMUNITY

(1) Formation →  A well developed plant community in any climate is called formation.

Eg.→ Tropical forest.

(2) Association →   A sub-unit of formation. A smaller community of plant formation with its two or more dominant species is known as association. A formation has many association.

(3) Consociation →  Sub unit of association, means a community with a single dominant species.

METHODS OF STUDY OF PLANT COMMUNITIES

1. Direct Method – This method is used to find out the species and members present in a community and study about them. This method can be used only for small community.

2. Sampling method – In this method we study the community in the form of sample. This method is also useful for large community. Samples are taken in the form of quadrats. The quadrats are formed with the help of rope to know the size of a quadrat, sequentially increase the size of quadrats according to increase in number of species, when the no. of the species becomes constant then estimate the number of plants present in the same size of quadrats. Then after that table work is done.

(i) Frequency →  No. of (Percentage) of samples on sampling unit in which species is present. It indicates species dispersal.

e.g. The plants of prosopis species were present in 90 samples out of 100 sample,

(ii) Density – The number of individuals per unit area, it indicates abundance of a species.

e.g. 10,000 prosopis were present in 100 sample

ANALYSIS OF PLANT COMMUNITIES:

Analysis of community characters is generally done for :-

•  Recording variations within and between communities.

•  Naming and classifying communities.

Community analysis involves measurements of various characters in sample plots or quadrats located with in the community.

Various community characters can be categorised as : 

(i) Analytic characters – Characters which are directly observed or measured in sample plots or quadrats.

(ii) Synthetic characters – Which are derived from the measurements of analytic chracters.

Analytic characters Synthetic characters 

• Frequency → Dispersion of species
  
  Note :- Frequency is an analytic character which show or indicate dispersion of species which is a synthetic character.

• Diversity → Relative abundance

• Biomass → Growth of plant

• Cover → Influence zone of species