We have tackled the big question of the origin of life on Earth and its evolution over in
the biology series. But how does this relate to ecology? For starters, the origin of life implies
the simplest, most ancient organism arising from non-living matter, and then subsequently evolving,
very gradually, over millions of years, into more complex organisms. These then formed populations,
communities, ecosystems, and then eventually the entire biosphere. Thus, the ecology connection.
So, just what is evolution in this ecological context? We can think of evolution as the
change in heritable traits, those traits that are transmissible from parent to offspring,
of biological populations over many generations. The process of evolution gives rise to diversity
at every level of biological organization. While studies in evolution consider the
processes by which modern organisms have developed from ancestral ones, the field of
ecology explores the interactive web of organisms and the environment. Organisms evolve because
they are in ecological relationships with other organisms of their environment and because the
environment itself influences their evolution via natural selection. So, even though we may think of
evolution as all the changes that took place over millions of years, the truth is that evolution is
at work all the time. Sometimes the changes are small and appear insignificant at first glance,
but they all play a part in natural selection and the survival of the species.
Speaking of natural selection, this is one of the many mechanisms of evolution. In most cases it
doesn’t lead to the development of a new species, it simply allows a species to better adapt to its
environment by changing the genetic make-up from one generation to the next. The organisms better
adapted to their environment tend to survive and produce more offspring, and this plays a role in
the evolution of beneficial features. If a species lacks a certain trait that will allow it to
survive, the species either dies out or eventually develops the missing trait. A modern example of
this is insects and our use of pesticides. The more a pesticide is used, the greater
the chance that the insects targeted will develop immunity to the chemical. Resistance can happen as
quickly as a single generation! Since many insects reproduce quickly, several generations can be born
within weeks and months, and by the time a few generations have passed, all insects are likely
to be resistant to the pesticide. Here’s another strange example. There are bacteria out there
called Pseudomonas that have evolved the ability to eat nylon. When placed in an environment where
only nylon was available as food, the bacteria evolved until it was able to eat it! This
demonstrates that even the most basic of lifeforms can adapt to the food an environment provides.
Another mechanism of evolution is mutation: or a change in the DNA sequence of an organism. This
can result due to errors in DNA replication during cell division, exposure to mutagens,
or high-energy radiation. Mutations generally fall into two types: point mutations, which
changes a single nucleotide, and chromosomal, or mutations that change chromosome structure.
Mutations can have a range of effects as well. Often, they can be harmful. Others have little or
no detrimental effect. And sometimes, although very rarely, the change in DNA sequence may
even turn out to be beneficial to an organism. More significant changes to organisms require
events like gene duplication or even chromosome duplication, followed by subsequent diversion from
the original copy through mutation, thus producing brand new proteins. This can also be achieved
through de novo genes, where a promoter migrates to a previously non-protein coding section,
thereby generating an entirely new gene. If these genes are involved with embryonic development,
we can see totally new body plans rapidly emerge. But this is more complex evolutionary biology
that is outside of the scope of this series. Now we arrive at mechanisms pertaining less
to biochemistry and more to ecology. The first is gene flow, also called gene migration. This is any
movement of individuals and the genetic material they carry, from one population to another,
changing the composition of the gene pool of the receiving population. Migrants can change
the distribution of genetic diversity by modifying allele frequencies, or the proportion of members
carrying a particular variant of a gene. This leads us to another mechanism of evolution,
genetic drift, which can lead to large changes in populations over a short period of time, though it
is a random process, not caused by environmental factors. In this case, allele frequencies of a
population change over generations due to chance, also called sampling error.
Essentially, an allele randomly starts to become more or less common in a population. When people
who have the gene causing a specific genetic trait like freckles, reproduce with people who do not
have the gene, the gene either can become more popular, such that nearly everyone gets freckles,
or totally disappear from the population, such that no one has freckles. While drift occurs
in all populations, its effects are strongest in the smallest populations. In natural populations,
all these mechanisms of evolution do not act in isolation, but rather in tandem at all times.
Finally let’s examine adaptations. In biology and ecology, adaptation refers to adjusting behavior,
physiology, or structure to become more suited for an environment. We covered these specifics in an
earlier tutorial, but it’s important to bring them up again, as understanding adaptations helps us
understand how some organisms can live in specific habitats. Mimicry, for example, is not just humans
imitating someone else in order to entertain. In biology, the close external resemblance of an
animal, plant, or part of one to another; as well as producing the same undesirable smells, sounds,
or behaviors as other creatures, can save the life of the imitator. We can see insects that strongly
resemble sticks and other such organisms which clearly benefit from this ability.
Toxin production is another adaptation critical to some plants, and these compounds act as a natural
defense mechanism against predators like insects or bacteria, as well as parasites and viruses.
These can be naturally occurring phytochemicals or metabolites formed by plants themselves
to protect against various threats. Amongst vertebrates, another adaptation is echolocation,
or a system of orientation involving the use of echoes or sounds produced by animals for
gathering information about its environment. This is performed in order to find roosts, or homes,
food, or both, irrespective of light conditions.
There are many more examples we could discuss, but an in-depth survey of the entire animal
kingdom in all of its incredible diversity can be found over in the zoology series, so if you want
to learn more about animals, head over there. For now let’s continue to learn about ecology.