Download Ecology - An Introduction Ecology comes from Greek root words

Ecology - An Introduction
Ecology comes from Greek root words oikos - home
and logos - to study.
Thus a definition:
Ecology is the study of the distribution and
abundance of species (or populations). It is also
the study of causes of those distributions and
abundances.
We can study distributions and abundances at many
levels:
at the population level
at the species level - a collection of populations
at the community level - where other species
interact with the one under study
at the ecosystem level - where we actively
consider the impact of the physical
environment on the species
at the biome level - combining many similar
ecosystems, e.g. temperate forests, deserts
at the biosphere level - combining all the
different ecosystems (or biomes) on earth.
1) the individual level - Adaptations in behaviour,
physiology & morphology; relations between
organisms and abiotic conditions are studied.
2) the population level - factors affecting population
size, density, and composition are the subjects.
We look at life histories, demography, and
interactions among individuals within
populations.
3) the community level - a community is the set
of populations of different species living in a
place. We study interactions among
populations and how they affect structure and
organization of communities
4) the ecosystem level - here we consider the
community in its abiotic context. Energy flow
through the set of populations and nutrient
cycling both among populations and into/out of
non-living components (soil, air,…) are included.
5) the landscape level - may not be completely
distinct from the ecosystem level, but it studies
different phenomena. At this level we look at
exchanges of organisms and materials between
habitats. It regards the environment as a mosaic,
and has been important in developing ideas about
how to conserve species.
6) the biosphere level - the biosphere is the sum of
all earth’s ecosystems.
If abiotic conditions are important in determining
where species live, what conditions are most
important?
Light, temperature, and precipitation
Light: (each sunbeam carries the same total energy)
Light intensity (energy/unit area) declines with
increasing latitude, thus temperature does as well. The
pattern is shown in Fig. 34.6A
Both light and temperature also vary seasonally.
Reason: the tilt of the earth’s axis with respect to its
orbit around the sun. At any given place on earth
(latitude) the angle at which sunlight strikes the
surface changes with the season. Our map latitude is
~42° N. That’s also ‘solar latitude’ at the equinoxes.
But on June 21 our ‘solar latitude’ is ~19° and on
December 21 it’s ~65°.
See Figure 34.6B
Sunlight heating the atmosphere (combined with the
rotation of the earth on its axis) explains winds and
precipitation patterns.
Air is heated most at the equator. It rises and cools.
Relative humidity rises. Rain results. In the upper
atmosphere this rising air spreads and cools. Cold,
dense air settles back toward the surface at around 30º.
It warms as it falls. Relative humidity decreases. Rain
is unlikely.
See Figure 34.6C
There are more such cells as you move to higher
latitude - 3 pairs in all.
These cells explain latitudinal patterns of rainfall, but
represent only vertical and north/south movements of
air. The earth rotates, and winds are deflected
east/west by the rotation. The deflections result from
the Coriolus effect.
Global wind and water circulation is driven by the
combined effect of atmospheric heating and rotation.
Local topography also influences precipitation. As air
rises over mountains, it cools, relative humidity rises.
At some altitude, the air becomes saturated, and it rains.
Over the mountain tops the air falls, it warms, relative
humidity drops, and rain is unlikely. Mountains cause
a rain shadow. This is the pattern at the Sierra Nevada
mountains of California.
See Figure 34.6F
Biomes
We divide the earth’s life forms into biomes. Each
biome represents a grouping of species at a fairly
large scale, but a grouping representing the kinds
of life found under a particular set of climatic
conditions.
We can divide the biomes into aquatic and terrestrial
ones. The aquatic biomes can be separated into
fresh water and marine types. Combined they cover
~75% of the earth’s surface.
The freshwater biomes:
1.Eutrophic lakes - nutrient rich, generally shallow,
with high rates of photosynthesis and high rates
of decomposition in the benthos (bottom). The
decomposition can cause anoxic conditions in
deeper parts of the lake.
2.Oligotrophic lakes - typically deeper, nutrient poor,
with low rates of photosynthesis, and a low
density of phytoplankton. With less
decomposition they are rarely anoxic.
Crater Lake in Oregon
3. The last type of freshwater biome is flowing water rivers and streams. In them there is a wide range of
communities, nutrient levels, and oxygen content.
What determines conditions is flow rate, the environment through which the water flows, and the
turbulence of flow.
There are transition zones between fresh water and
marine ecosystems. They are called estuaries. They
are typically nutrient rich and among the most
productive places on earth. Along Chesapeake Bay
and much of the Everglades are large estuaries.
There are also transition zones between fresh water
and terrestrial ecosystems. They are called wetlands
(marshes, bogs, and fens). Part of Point Pelee park and
much of the Walpole Island Reservation is wetland.
Marine communities are divided by physical criteria depth, light penetration, and distance from shore. Here
is a map of the zones:
At the shoreline is a region called the intertidal zone.
Here organisms may be exposed as the tide goes out
and submerged when it comes in. Different kinds of
organisms and different species within groups are
adapted to the different degrees of exposure of upper,
mid-, and lowermost zones of the intertidal.
The terrestrial biomes are more diverse. Here is a
map of the major terrestrial biomes:
Tropical forest – one of the most diverse community
types on earth. It occurs only where rainfall exceeds
2500mm per year; temperature is >18ºC and changes
<3ºC during the year). Trees do not lose their leaves
at any given time of the year, though there may be a 3
month season of lower rainfall. Soils are nutrientpoor, since nutrients are bound up in living tissues.
Deserts – have dry climates year-round. Most
deserts are found near 30ºN or S latitude. The
common image is of the Sahara that is nearly devoid
of vegetation. However, deserts can have diverse
flora and fauna that are adapted to dry conditions in
various ways (e.g. cactuses have needles instead of
leaves, desert rodents exude a urine that is
concentrated uric acid, enormously reducing
water loss).
Tundra – a Russian word meaning treeless plain.
The community lives above permanently frozen
ground (permafrost). It is quite wet. Though rainfall
is not high, permafrost prevents rain from percolating
down through the soil; it puddles and ponds. The
growing season is short, no more than 2 months.
Plants and animals adapt to the short season.
Boreal forest – in Russian, called taiga. These are the
coniferous forests between temperate deciduous
forest and tundra. Summer is relatively short, winter
long and cold. Evergreen trees have the energetic
advantage of not having to develop new leaves each
year. There are fewer insects than at lower latitude,
and plants are mostly wind-pollinated.
Temperate grassland (prairie) – temperate
communities where limited precipitation (generally
25 -75cm/yr) limits the growth of trees, which are
rare. Typically far removed from large bodies of
water, and towards the center of continents. This is
the biome altered by human activity to develop land
for agriculture. Plants are adapted for herbivory
(e.g. bison).
Chapparral – occurs where there are winter rains and
summer drought (a Mediterranean climate). Typically
treeless, with grasses and shrubs. Shrubs are adapted
to the low rainfall, with sclerophyllous (leathery)
leaves that limit water loss. The community is also
adapted for the frequent fires that ignite during the dry
summer.