Interactions Between Organisms And It’s Environment

Date: January 25, 2018

Organism Physical Environment Biotic and Abiotic factors

Interactions Between Organisms And It’s Environment

In previous updates from Ecology we have now established that the physical (abiotic components like rain, waterfall, wind, humidity) factors of environment influence the survival of an organism (biotic component of environment). Here we will discuss both scenarios delineating Interactions between organisms and it’s environment.

  1. Components of environment influencing organism: Every aspect of environment has its impact on the basic unit of ecology i.e. organism in various aspects.
  2. Temperature: Prime environmental component influencing an organism is Temperature it thrives in. The average temperature on land varies seasonally, decreases progressively from the equator towards the poles and from plains to the mountain tops. It ranges from subzero levels in polar areas and high altitudes to >500C in tropical deserts in summer. The significance of temperature for an living organisms is understood by the fact that it affects the kinetics of enzymatic reactions happening inside its body, thus affecting basal metabolic rate, thus have implications on physiological functions of the organism. Depending upon the temperature ranges the organisms live they are referred to as eurythermal (can tolerate and live in wide range of temperatures) or stenothermal (can tolerate and live in a short range of temperature variations) Fig 1. This capability of temperature tolerance fully determines the geographical distribution of species.
  3. Water: Next to temperature, water is the most important factor influencing the life of organisms. Being the universal solvent, water entirely owns the creation of life on earth and its sustainability. Plants and animals are completely dependent on water for their growth, reproduction, and overall survival. Even for aquatic living organisms salinity, pH, and ion gradient of water body they live in is crucial. In fact, life on earth originated in water and is unsustainable without water. Its availability is so limited in deserts that only special adaptations make it possible to live there. The productivity and distribution of plants is also heavily dependent on water. Some organisms are tolerant of a wide range of salinities (euryhaline) but others are restricted to a narrow range (stenohaline) Fig 2.
  4. Light: Since plants produce food through photosynthesis, a process which is only possible when sunlight is available as a source of energy, we can quickly understand the importance of light for living organisms, particularly autotrophs. Many species of small plants (herbs and shrubs) growing in forests are adapted to photosynthesise optimally under very low light conditions because they are constantly overshadowed by tall, canopied trees. Many plants are also dependent on sunlight to meet their photoperiodic requirement for flowering. For many animals too, light is important in that they use the diurnal and seasonal variations in light intensity and duration (photoperiod) as cues for timing their foraging, reproductive and migratory activities. The availability of light on land is closely linked with that of temperature since the sun is the source for both. But, deep (>500m) in the oceans, the environment is perpetually dark and its inhabitants are not aware of the existence of a celestial source of energy called Sun. The spectral quality of solar radiation is also important for life. The UV component of the spectrum is harmful to many organisms while not all the colour components of the visible spectrum are available for marine plants living at different depths of the ocean.
  5. Soil: The nature and properties of soil in different places vary; it is dependent on the climate, the weathering process, whether soil is transported or sedimentary and how soil development occurred. Various characteristics of the soil such as soil composition, grain size and aggregation determine the percolation and water holding capacity of the soils. These characteristics along with parameters such as pH, mineral composition and topography determine to a large extent the vegetation in any area. This in turn dictates the type of animals that can be supported. Similarly, in the aquatic environment, the sediment-characteristics often determine the type of benthic animals that can thrive there.
  6. Changes in organisms with respect to Environment: As discussed, organisms are completely dependent on their environment for regulation of all physiological functions and overall survival. How organisms adjust to these sets of conditions is described here.
  7. Regulate: Some organisms are able to maintain homeostasis by physiological (sometimes behavioural also) means which ensures constant body temperature, constant osmotic concentration, etc. All birds and mammals, and a very few lower vertebrate and invertebrate species are indeed capable of such regulation (thermoregulation and osmoregulation). We maintain a constant body temperature of 370C. In summer, when outside temperature is more than our body temperature, we sweat profusely. The resulting evaporative cooling, similar to what happens with a desert cooler in operation, brings down the body temperature. In winter when the temperature is much lower than 370C, we start to shiver, a kind of exercise which produces heat and raises the body temperature. Plants, on the other hand, do not have such mechanisms to maintain internal temperatures.
  8. Conform: An overwhelming majority (99 per cent) of animals and nearly all plants cannot maintain a constant internal environment. Their body temperature changes with the ambient temperature. In aquatic animals, the osmotic concentration of the body fluids change with that of the ambient water osmotic concentration. These animals and plants are simply conformers. Thermoregulation is energetically expensive for many organisms. This is particularly true for small animals like shrews and humming birds. Heat loss or heat gain is a function of surface area. During the course of evolution, the costs and benefits of maintaining a constant internal environment are taken into consideration. Some species have evolved the ability to regulate, but only over a limited range of environmental conditions, beyond which they simply conform Fig 3.
  9. Migrate: The organism can move away temporarily from the stressful habitat to a more hospitable area and return when stressful period is over. Many animals, particularly birds, during winter undertake long-distance migrations to more hospitable areas. Every winter the famous Keolado National Park (Bharatpur) in Rajasthan host thousands of migratory birds coming from Siberia and other extremely cold northern regions.
  10. Suspend: In bacteria, fungi and lower plants, various kinds of thickwalled spores are formed which help them to survive unfavorable conditions – these germinate on availability of suitable environment. In higher plants, seeds and some other vegetative reproductive structures serve as means to tide over periods of stress besides helping in dispersal – they germinate to form new plants under favourable moisture and temperature conditions. They do so by reducing their metabolic activity and going into a state of ‘dormancy’. In animals, the organism, if unable to migrate, might avoid the stress by escaping in time. The familiar case of bears going into hibernation during winter is an example of escape in time. Some snails and fish go into aestivation to avoid summer–related problems-heat and dessication. Under unfavourable conditions many zooplankton species in lakes and ponds are known to enter diapause, a stage of suspended development.
  11. Adapt: adaptation is any attribute of the organism (morphological, physiological, behavioural) that enables the organism to enhance its survival and reproductive strategies. Many adaptations have evolved over a long evolutionary time and are genetically fixed. Classic examples being: hump of a camel and present of thrones on cactus plant.