ECOLOGY

by Purwaning Rohmah/BIO off A 2015 UM

TOLERANCE RANGE OF SPECIES

Life is found almost everywhere on Earth, but it is not distributed evenly around the planet. Different species are found in different areas; some species have overlapping ranges which is called by first word of “eury”, others do not which is called by first word “steno”. Each species has their own environmental conditions within which it can best survive and reproduce. Not surprisingly, those conditions are the ones for which it is best adapted. Many different physical, abiotic (non-living) factors influence where species live, including temperature, humidity, soil chemistry, pH, salinity and oxygen levels.

Just as species have geographic ranges, they also have tolerance ranges for the abiotic environmental conditions. In other words, they can tolerate (or survive within) a certain range of a particular factor, but cannot survive if there is too much or too little of the factor. Take temperature, for example. Polar bears survive very well in low temperatures, but would die from overheating in the tropics.

  

         Polar bears                               Giraffes

On the other hand, a giraffe does very well in the heat of the African savanna, but would quickly freeze to death in the Arctic. This example points out an important aspect of tolerance ranges – different types of organisms have different tolerance ranges for the same factor. And in fact, the tolerance range of a single individual may change over time; individuals of a certain species of salmon, for example, start life in a freshwater stream, migrate out to the open ocean, and then come back to their home stream to reproduce. The salmon tolerates huge changes in the salinity (salt content) of the various water it passes through during its journey, and also experiences many changes in water temperature.

Those examples can be shown in the diagram of fish thermal tolerance range below:

The abundance of organisms are very high in the optimum temperature tolerance range which means it is the match maximum rate of organism can grow and reproduce well. That’s why there are so many amount of the species in this zone. As the gradient goes lower or higher, so does the rate of the growth and reproduction. When the abiotic factor (in this discussion is temperature) still can be tolerated by the organism but it is ot the optimal range for their growth and reproduce, the presence of the species will be much lower. This zone called zone of physiological stress. When the gradient goes lower or higher again until ino presence of this organism, it called zone of intolerance.