Heliophytes are those plants which grow in strong light so are commonly called Sun plants e.g. sunflower, while sciophytes are those plants which prefer to grow in lower light intensities or shade loving plants e.g. money plant, fir etc. 

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. five closely related species of warblers living on the same tree have been shown to coexist and avoid competition by behavioural differences in their foraging activities

Heat loss or heat gain is a function of surface area.
Since small animals (like humming birds) have a larger surface area relative to their volume, they tend to lose body heat very fast, when it is cold outside.
They spend more energy to generate body heat through metabolism; considering the cost and benefit of maintaining   a constant internal temperature, small animals (humming birds) are not found in polar regions.

Ways to adapt unfavourable conditions are:
(i) Snails undergo aestivation (summer sleep) to avoid summer related problems.
(ii) Bears undergo hibernation (winter sleep) during winter.
(iii) Zooplanktons enter a stage of suspended development called diapause.
(iv) Bacteria and fungi slow down their metabolic rate and from thick-walled spores germinate when the conditions become suitable.

Reproductive strategies:
(i) Some organisms breed only once in their life time-e.g. Bamboo, Pacific Salmon.
(ii) Some produce a large number of small-sized offspring-Oysters.
(iii) Some breed many times during their life time-e.g. birds.
(iv) Some produce a small number of large sized offspring, e.g. Mammals.

(i) Tropical rainforest    
(ii) Deciduous forest    
(iii) Desert    
(iv) Coniferous forest    
(v) Agricultural fields    
(vi) Grassland.

Initially, after a lag phase, the population will grow in an exponential manner as the nutrients and space will be abundant. When the food sources get depleted, the population density starts decreasing and ends in an asymptote phase, then the population density reaches the carrying capacity (maximum number of given environment can sustain indefinitely).
The population shows a pattern of logistic growth giving an S-shaped curve. where, K-carrying capacity, N=population density at time 't', r = Intrinsic rate of natural increase

Commensalism:
Commensalism is defined as an interspecific interaction where one species is benefitted, while the other species is neither benefitted nor harmed, e.g.
(i) Orchids grow as epiphytes on mango 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