Evolution and Biodiversity - Environmental Science - page 67

Three conditions are necessary for evolution of a
population by natural selection to occur. First, there
must be genetic variability for a trait in a population.
Second, the trait must be heritable —that is, it can be
passed from one generation to another. Third, the trait
must lead to differential reproduction —that is, it
must enable individuals with the trait to leave more
offspring than other members of the population. Note
that natural selection acts on individuals, but evolu-
tion occurs in populations.
An adaptation, or adaptive trait, is any heritable
trait that enables an organism to survive and repro-
duce better under prevailing environmental condi-
tions. Structural adaptations include coloration (allow-
ing more individuals to hide from predators or to
sneak up on prey), mimicry (looking like a poisonous
or dangerous species), protective cover (shell, thick skin,
bark, or thorns), and gripping mechanisms (hands with
opposable thumbs; see Figure 4-1). Physiological adap-
tations include the ability to hibernate during cold
weather and give off chemicals that poison or repel
prey. Behavioral adaptations include the ability to fly to
a warmer climate during winter and various interac-
tions between species.
When faced with a change in environmental con-
ditions, a population of a species has three possibili-
ties: adapt to the new conditions through natural
selection of an increasing number of individuals in the
population, migrate (if possible) to an area with more
favorable conditions, or become extinct.
The process of microevolution can be summarized
as follows: Genes mutate, individuals are selected, and
populations evolve.

pulses of sound. They analyze the returning echoes to
create a sonic “image” of their prey. (We have copied
this natural technology by using sonar to detect sub-
marines, whale, and schools of fish.)
As a countermeasure, some moth species have
evolved ears that are especially sensitive to the sound
frequencies that bats use to find them. When the moths
hear the bat frequencies, they try to escape by falling to
the ground or flying evasively.
Some bat species evolved ways to counter this de-
fense by switching the frequency of their sound
pulses. In turn, some moths evolved their own high-
frequency clicks to jam the bats' echolocation system
(we have also learned to jam radar). Some bat species
then adapted by turning off their echolocation system
and using the moths' clicks to locate their prey.
As we see, each species continues refining its adap-
tations in this ongoing coevolutionary contest. Coevo-
lution is like an arms race between interacting popula-
tions of different species. Sometimes the predators
surge ahead; at other times the prey get the upper hand.

4-3 ECOLOGICAL NICHES
AND ADAPTATION

Ecological Niches
Each species in an ecosystem has a specific role
or way of life.
If asked what role a certain species, such as an alliga-
tor, plays in an ecosystem, an ecologist would describe
its ecological niche, or simply niche (pronounced
“nitch”). It is a species' way of life or functional role in
a community or ecosystem and involves everything
that affects its survival and reproduction.
The ecological niche of a species differs from its
habitat, the physical location where it lives. Ecologists
often say that its niche is analogous to a species' occu-
pation, whereas its habitat is analogous to its address.
A species' fundamental niche consists of the full
potential range of physical, chemical, and biological
conditions and resources it could theoretically use if it
could avoid direct competition from other species. Of
course, in a particular ecosystem, different species of-
ten compete with one another for the same resources.
In short, the niches of competing species overlap.
To survive and avoid competition for the same
resources, a species usually occupies only part of
its fundamental niche in a particular community or
ecosystem—what ecologists call its realized niche. By
analogy, you may be capable of being president of
a particular company (your fundamental professional
niche ), but competition from others may mean you
become only a vice president (your realized professional
niche ).

How many moths can you eat? Find out and learn more
about adaptation at Environmental ScienceNow.

Coevolution: A Biological Arms Race
Interacting species can engage in a back-and-forth
genetic contest in which each gains a temporary
genetic advantage over the other.
Some biologists have proposed that interactions between
species can result in microevolution in each population.
According to this hypothesis, when populations of two
different species interact over a long time, changes in
the gene pool of one species can lead to changes in the
gene pool of the other. This process is called coevolu-
tion. In this give-and-take evolutionary game, each
species is in a genetic race to produce the largest num-
ber of surviving offspring.
Consider the interactions between bats and moths.
Bats like to eat moths, and they hunt at night and use
echolocation to navigate and locate their prey. To do
so, they emit extremely high-frequency, high-intensity