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Ecology

Perhaps the strongest influences on any of these is climate (or more specifically precipitation and temperature) but species survival is influenced by many other abiotic factors such as sunlight, seasonality, soils, disturbance and fire. Biotic interactions also include predation, competition, dispersal, and synergism.

The expression of survival within all rainforest biota can be recognised in their adaptations (be they physical or physiological) some of which relate to the unique features of rainforest plants. However, this is by no means comprehensive of the physical adaptations let alone the larger interactions of rainforest life! 

To give an idea of the complexity of ecology in the rainforest we have put together a few examples of how different abiotic and biotic features influence life around them. 

Seasonality, which besides influencing the precipitation and temperature of a rainforest, also influences whether vegetation is evergreen or deciduous. This in turn influences stratification, whereby light gaps open for a period during the loss of leaves, allowing more herbaceous species to survive on the rainforest floor. This could then be seen to promote the occurrence of ground-dwelling herbivores, who in more seasonal rainforests, would require the ability to climb into trees to obtain food. Seasonal rainforests also tend to have more migratory species which move on at times of the year when limited food is available1, 2

Disturbance, such as the collapse of a tree within the rainforest allows more sunlight onto the forest floor, thus increasing the temperature of the soil. Not only does the gap then allow for the succession of a new rainforest plant, but the increased irradiance and soil temperatures can break the dormancy of seeds in the seed bank leading to germination and an increase in the seedling bank3. Disturbance on a larger scale such as that which might be caused by fires, can also influence succession by removing fire sensitive rainforest species and promoting those that can survive. This may also equate to the complete loss of rainforest and replacement with other fire dependant vegetation types. Disturbance that leads to the loss of rainforest can influence subsequent dispersal of species between remaining remnants as pollinators and dispersal agents (insects, birds, animals) may not move between populations, limiting recruitment1, 2, 4, 5, 6

Topography also has a strong influence on rainforest ecology due to the amount of moisture present within a site by controlling water run-on and run-off rates and the rate of evaporation depending on the site aspect. Soil moisture subsequently influences the species that may successfully live on a site and the degree of competition (for water resources) between them. Topography, and specifically elevation, also influence species distributions by way of temperature whereby higher elevations are cooler and usually less species diverse. Cool temperatures also result in slower rates of decomposition thus influencing soil fertility, which is also influenced by topography by the movement into (deposition) or removal of (erosion) soil particles. Soil fertility is a key driver of species distributions in Australian rainforests4.
 
  1. Richards, P (1996) The Tropical Rain Forest: An Ecological Study. (2nd) Cambridge University Press, UK
  2. Whitmore, T. (1990) An Introduction to Tropical Rain Forests. Oxford University Press, New York, USA.
  3. Batlla, D. and Benech-Arnold, R. (2014) Weed seed germination and the light environment: implications for weed management. Weed Biology and Management. 14, 77-87.
  4. Kitching, R., Braithwaite, R., Cavanaugh, J. (2010) Remnants of Gondwana: A natural and social history of the Gondwana Rainforest of Australia. Surrey Beatty & Sons, Baulkham Hills NSW Australia.
  5. MacDermott, H., Fensham, R., Hua, Q., Bowman, D. (2017) Vegetation, fire and soil feedbacks of dynamic boundaries between rainforest, savanna and grassland. Austral Ecology. 42, 154-164.
  6. Murphy, B., Bowman, D. (2012) What controls the distribution of tropical forest and savanna? Ecological Letters, 15, 748-758.
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