Encyclopedia of Evolution.pdf - Online Reading Center

0 ecology
Second, organisms can conduct kinetic energy into the air or
water around them. Third, plants and animals on dry land can
evaporate water. A great deal of energy is required to evaporate
water, therefore evaporation (transpiration from plants,
perspiration from animals) is a very efficient cooling mechanism.
The evolution of each species has been influenced by the
necessity of maintaining energy balance. For example, desert
bushes have evolved small leaves that allow them to disperse
more of their heat load in the form of kinetic energy rather
than the evaporation of water, which is rare in their habitats.
At the same time, these bushes have often evolved deep roots,
which maximize the amount of water they can obtain. Plants
and animals from separate evolutionary lineages have often
evolved similar adaptations to these climatic conditions (see
convergence). Animals need to increase their energy loss in
hot environments and restrict it in cold environments. Warmblooded
animals have evolved thick layers of hair or fat to
insulate them in cold environments. Hibernation is an evolutionary
adaptation that allows animals to avoid excessive
energy loss during winter.
The temperature and rainfall patterns of different parts
of the Earth are influenced by the movements of the Earth,
as well as the arrangement of the continents. Before the Pleistocene
epoch (see Quaternary period), oceanic currents
carried warm water into North Polar regions, making them
much warmer than they are today. The movement of continents
subsequently closed off some of this circulation, causing
the North Polar region to become permanently cold and
beginning a cycle of ice ages (see continental drift).
II. Obtaining matter. Organisms not only need energy but also
need matter. Photosynthesis removes carbon dioxide gas from
the air or water and makes sugar from it. Animals and decomposers
obtain matter from the food chain at the same time and
from the same sources that they obtain energy. All organisms,
including plants, release carbon dioxide gas back into the air
or water. Organisms also need nitrogen and minerals such
as phosphorus, potassium, and calcium. Plants obtain them
mostly from the soil by absorbing inorganic chemicals with
their roots. Plants store some of these minerals and use others
in the construction of their large organic molecules. Animals
and decomposers obtain minerals from their food.
Synecology
I. Interactions within populations. A population is all of the
individuals of a species that interact. Populations can grow
exponentially because of the reproduction of the individuals
that make it up. Species have evolved different reproductive
systems that allow individuals to successfully produce
offspring and disperse them into new locations. Populations
also contain genetic variability (see population genetics),
which is essential for natural selection. Natural selection
occurs within populations, and the reproductive success (fitness)
of an individual is relative to the other members of the
population. Individuals compete with one another not only
for resources such as food and territory but also for opportu-
nities to mate (see sexual selection). Different populations
in a species can become new species (see speciation). Practically
every aspect of evolution is influenced by the synecology
of populations.
II. Interactions between species. Species have evolved to use
one another in many different ways. The food chain has
already been mentioned. Since evolution has produced millions
of species, each of which makes its living in a slightly
different way, evolution has produced many complex interactions
among species. Plant species have evolved different
ways of protecting themselves from herbivores, including
thousands of kinds of toxic chemicals, and herbivores have
evolved ways of getting around the plant defenses. Prey animals
have evolved many ways of protecting themselves from
predators, and predators have evolved many ways of finding
and eating the prey. Many animals obtain their food by
pollinating the plants that have made use of those animals to
transport their pollen. Many species have evolved very close
relationships, called symbioses, in which the other species is
the most important environmental factor. In many cases, symbioses
have evolved toward the mutual benefit of both species
(mutualism). Many ecological interactions have resulted from
coevolution. In some cases, one species has evolved such a
dependence on another that its individuality has been lost and
the two have fused into one (see symbiogenesis).
III. Ecological communities. The total of all the interspecific
interactions in a location is the ecological community. This is
the context within which all evolutionary change occurs. Evolution
has produced a great diversity of species within each
community (see biodiversity). Biodiversity results from a
balance between speciation and extinction. The movements
of continents not only influence the climate, as explained
above, but also separate species and bring species together,
allowing new interactions to occur and new biodiversity to
evolve. When new islands emerge from the ocean, new species
quickly evolve (see biogeography). Disturbances such as
fire and storm occur within ecological communities, which are
disastrous to some individuals, but create openings that can be
colonized by others. Species diversity has been much enhanced
by the evolution of species that specialize on disturbed areas.
Many human activities create disturbances. The disturbances
created by humans, however, may be occurring more rapidly
than ecological communities or the evolutionary process can
handle, with the result that human activity may now be causing
the sixth of the Earth’s great mass extinctions.
IV. Ecosystems. An ecosystem is an ecological system that
incorporates the ecological community with the flow of energy
and cycling of matter. Ecosystem ecology ties together autecology
and synecology by considering both organisms and the
nonliving environment as components of an interacting system.
At every level, from the energy balance of an individual
organism to the interactions of all the species in the world,
evolution occurs within an ecological context and has made