All living organisms exhibit some level of sensitivity to their environment because they need to sense and respond to their surroundings in order to survive and thrive. Sensitivity to environmental changes is a fundamental aspect of life. However, the degree of sensitivity can vary significantly among different organisms, and some are more sensitive than others.

Microorganisms, particularly certain bacteria and archaea, are often considered among the most sensitive organisms to environmental changes. This sensitivity is because they are typically exposed directly to their surroundings and lack protective structures like the tissues and organs found in multicellular organisms. As a result, they can be highly responsive to changes in factors such as temperature, pH, salinity, and the presence of chemicals. Some microorganisms, known as extremophiles, are adapted to thrive in extreme conditions but can still be sensitive to even small variations in those extreme environments.

In contrast, larger and more complex organisms like mammals, including humans, have evolved more sophisticated mechanisms for buffering themselves from immediate environmental changes. For example, humans can regulate their body temperature, blood pH, and other internal conditions within narrow ranges even when external conditions vary. However, even these more complex organisms are sensitive to environmental changes, and extreme or prolonged changes can have adverse effects on their health and well-being.

In summary, all living organisms are sensitive to some extent to their environment, but the degree of sensitivity varies, with microorganisms often being among the most sensitive due to their direct exposure to external conditions.

Dr Gaurav H Tandon thank you for your contribution to the discussion

There are facies-critical/sensitive fossils useful for an environment analysis based on organic matter, and there are also fossils uncritical to facies changes and thus left unaffected by facies changes. These are the best ones for biostratigraphy and chronology.

For more information you must consult the “Treatise of invertebrate paleontology”. The number of genus and species is countless.

HGD

Dr Harald G Dill thank you for your contribution to the discussion

Amphibians are small vertebrates that need water, or a moist environment, to survive. The species in this group include frogs, toads, salamanders, and newts. They are sometimes called "indicators." They are called indicators because they are very sensitive to change in their environment. Living things can sense what is going on around them, and are able to respond to it. This is known as sensitivity. Animals have sense organs, such as eyes, that tell them what is going on outside their bodies. Living things are sensitive and responsive to stimuli. Non-living things are not sensitive and do not respond to stimuli. Living organisms have the ability to sense their surroundings or environment and respond to these environmental stimuli which could be physical- chemical or biological. Living organisms sense their environment through sense organs. Living things are able to sense their surroundings. As, a living thing can respond to a change in sound, heat, or light. Living things can respond to changes in the environment they live in. Some living things are very sensitive. In ecology, these are called indicator species. This means they can tell scientists whether the environment they live in is a healthy one. “Sensitivity leads to inner strength, the ability to realize what's going on with you and others at that moment.” Sensitive individuals who are more aware of what's going on in the moment have the capacity to open their minds and bodies to the world around them. Hence, it is clear from the above points that Amphibian is most sensitive to environmental change. Insects, reptiles and many other animals are often referred to as being 'cold-blooded' because, unlike mammals and birds, their body temperature fluctuates with the temperature of their surrounding environment. As a result, many cold-blooded animals are very sensitive to changes in local climate. Primates, elephants and marsupials including kangaroos, wallabies and koalas are the mammal species groups found to be most threatened by a changing climate. The slow reproductive rates of primates and elephants further increase their vulnerability. Climate change also alters the life cycles of plants and animals. For example, as temperatures get warmer, many plants are starting to grow and bloom earlier in the spring and survive longer into the fall. Some animals are waking from hibernation sooner or migrating at different times, too