(i) In some shallow South American lakes, visiting flamingoes and resident fishes compete for their common food, zooplanktons.
(ii) Abingdon tortoise of Galapagos island became extinct when goats were introduced into the island,

Predators 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 a predator. When all the starfish was removed experimentally, more than 10 species of invertebrates became extinct within a year, because of interspecific competition.

Sex ratio refers to the ratio between the number of males and the number of females of a given population, at a given time.  It is characteristic of a population.

Larger animals such as birds and mammals are able to maintain body temperature by physiological means.These have more volume and smaller surface area as compared to smaller animals.

Acclimatization. The gradual physiological adjustment to shoe changing environmental conditions is called acclimatization.
Ectotherms are the cold-blooded animals who can not regulate their body temperature.
Endotherms are the warm-blooded animals who are capable of regulating their body temperatures.

(a) A - Expanding, B - Stable, C- Declining.
(b) Stable population is preferred. It is helpful for planning any welfare activity.
(c) Logistic growth curve.

(a) Adaptations of desert plants and animals.
Adaptations of desert animals.
1. Animals faced with water scarcity as found in arid or desert areas, show two types of adaptations, reducing water loss and ability to tolerate arid conditions KangaroolDesert Rat seldom drinks water. It has a thick coat to minimise evaporative desiccation. The animal seldom comes out of its comparatively humid and cool burrow during the day time. 90%of its water  requirement is met from metabolic water (water produced by respiratory breakdown) while 10% is obtained from food.
2. Loss of water is minimised by producing nearly solid urine and feces.
3. Spiny skin and highly cornified in Phrynosoma (horned toad) and Maloch horridus.
Adaptations of desert plants.
1. Plants have thick cuticle, succulent organs where water and mucilage are stored.
2. Stomata are sunken.
3. They have well developed branched root system.
4. They possess waxy coating on surface.
5. Crassilucean pathway of photosynthesis.
6. They \({ C }_{ 4 }\) are  plants.
(b) Adaptations of plants to water scarcities. They are called xerophytes. The above mentioned adaptation of plants are applicable (see part (a)))
(c) Behavioural adaptations in animals.
(i) Hibernation
(ii) Aestivation
(iii) Periodic activity
(iv) Camouflage migration.
(d) Importance of light to plants.
(1) Source of energy
(2) Photoperiodism
(3) Pigmentation
(4) Daily rhythm
(5) Plant movements and
(6) Growth.
(e) Effect of temperature or water scarcity and adaptation of animals. As discussed in(c) and reducing loss of water from body, and ability to tolerate arid condition.

(i) Predation acts as a conduit for energy transfer across trophic levels.
(ii) It keeps the prey population under control.
(iii) It helps in maintaining species diversity in a community, by reducing the intensity of competition.
(iv) Biological control of pests is based on the principle of predation.

Symptoms include:
(i) nausea
(ii) fatigue, and
(iii) heart palpitations.
Adaptations are:
(i) Increase in breathing rate.
(ii) Increased production of red blood cells.
(iii) Decreasing binding capacity of haemoglobin.

(i) Population attributes are certain characteristic of a population. Some of them are as follows:
(a) Population size or density is the number of individuals of a species per unit area or volume.
Population Density
\((PD)=\frac { Number\quad of\quad individuals\quad in\quad a\quad region\quad (N) }{ Size\quad of\quad unit\quad area\quad in\quad the\quad region\quad (S) } \)
\(\\ or, \quad PD\quad =\quad \frac { N }{ S } \)
(b) Birth rate or natality is expressed as the number of births per 1000 individuals of a population per year, e.g. if in a pond, there are 20 lotus plants last year and through reproduction 8 new plants are added
Birth rate = \(\frac { 8 }{ 20 } \) = 0.4 offspring per lotus per year
(c) Death rate or mortality is expressed as the number of deaths per 1000 individuals of a population per year, i.e. if 4 individuals in a population of 40 fruitflies died during a specified time interval (say a week).
Death rate =\(\frac { 4 }{ 40 } \)=0.1 individuals per fruitfly per week
(d) Sex ratio is expressed as the number of females and males per 1000 individuals of a population in a given time, e.g. 60% females and 40% males in population.
(e) Age pyramid When the age distribution (percent individuals of a given age or age group) is plotted for the population, this is called age pyramid.
(ii) Population density is the number of people living per unit of an area.
Three ways of measuring population density of a habitat.
(a) Biomass or percentage cover, e.g. hundred Parthenium plants and one huge banyan tree.
(b) By measuring relative density, e.g. the number of fish caught per trap from a lake.
(c) Indirect estimation, e.g. without seeing or actually counting population sizes, e.g. the tiger census is often based on pug marks and faecal pellets.

(a) Commensalism
(b) (i) Orchids grow as epiphytes on mango tree or other fruit trees.
Orchids are benefitted by getting a shelter, while the tree is neither benefitted nor damaged.
(ii) Barnacles growing on the whale are benefitted to move where food is available.
(iii) The cattle egrets always forage near to where the cattle animals graze; the cattle animals stir up the ground and the insects are flushed out from the vegetation and make it easy for the egrets to catch them.
(iv) The clown fish living among sea anemones get protection from their predators, which stay away from the stinging tentacles of the sea anemone:
(c) Amensalism
Roots of certain plants secrete chemicals, which are harmful to the soil organisms.
The antibiotics secreted by certain soil fungi are harmful to soil fungi bacteria. (anyone)
(d) Interactions should be beneficial to all concerned. Avoid selfish or selfcentered people.

(a) The factors include
(i) The rotation of the earth around the sun and the tilt of its axis cause annual variation in the intensity and duration of temperature, which affects distinct reasons.
(ii) Annual variation in precipitation.
(b) (i) Scorching deserts of Rajasthan.
(ii) Rain-soaked Meghalaya forests
(iii) Deep ocean trenches.
(iv) Tropical rain forests
(v) High mountain tops. (any four)
(c) Interactions are necessary; they should be beneficial to all.