Biodiversity – Dec. 3/12
- As we move from the poles towards the equator we know (from observation) that the amount of
solar energy per unit area increases (due to the curvature of the earth) and the yearly seasonal
variation decreases (due to tilt of earth’s axis of rotation). Therefore, the tropics has the most amount
of solar energy per unit area and the least amount of seasonal variation in solar energy throughout
the year. The total number of species per unit area increases from the poles towards the equator.
- Latitudinal gradient in species diversity: Localities at lower latitudes have more species than
localities at higher latitudes. Species richness increases towards the equator. Species richness is the
total number of species in a given area. This is one of the most widely recognized patterns in
- Terrestrial biomes: The temperate deciduous forest (TDF) has a greater species richness compared
to the boreal forest, and the tropical forests have a greater species richness compared to the TDF and
the greatest species richness of all localities on earth.
- Temperate deciduous forest (TDF): This is found here in London. TDF is found here, in eastern US, in
Europe, and in part of Asia. The vegetation is dominated by broadleaf deciduous trees. They drop all
their leaves in the fall. Some are conifers. There are four distinct seasons in this biome. There is
moderate annual average temperature and moderately high annual precipitation (90-150cm).
Canada has the most species rich ecosystem of the places with temperate deciduous forest. In
Canada, this ecosystem is also called the eastern deciduous forest or the Carolinian zone. The north
shore of Lake Erie is the most species rich area in Canada. Deep, nutrient rich soil is found in TDF.
The dominant flora in the TDF is broad-leaved deciduous trees (maple, oak, beech, ash, hickory, tulip
tree). They have large, flat leaves. We don’t actually see this much diversity any more, but there is a
large diversity of trees that would occur in undisturbed forest. The maple tree (genus Acer) is a
native species of this biome. There is dramatic change in the temperate deciduous forest throughout
the year. Leaves that drop to the ground decompose and add nutrients to the soil.
- Insects in the temperate deciduous forest spend the winter in either the egg, larval, nymphal, pupal,
or adult stage (depending on the species) in a dormant (most) or active (some) state. Insects have
adaptations to seasonality. They find a protected place, for example, leaf litter, soil, under bark or
rock, dead wood. Dead wood is essential for larvae during growing seasons and as an overwintering
site in the winter.
- Tropical forests: A lack of seasonality is the difference between tropical and temperate forests.
- Characteristics of the tropics: It is located between the tropics of Cancer and Capricorn. Day length is
more or less constant throughout the year (12/12). The climate is warm (not extremely hot) and
there is little fluctuation in temperature, with 23-27ᵒC year round. There can be great fluctuation in
rainfall throughout the year depending on the location. Many distinct ecosystems occur in the tropics.
Some parts of the tropics have distinct 6-month wet and dry seasons (tropical dry forest). Others
have more constant rain throughout the year (tropical wet/humid/rain forest).
- Tropical rain forest (TRF): This biome has the highest amount of precipitation (rainfall) with at least
200cm annually. There is little seasonal variation in rainfall. This is the biome with the greatest
species richness on earth. It is home to at least half of all plant and animal species on earth. It covers
7% of the earth’s surface area. It is the most complex ecosystem due to interactions between so many
species. It has the greatest biodiversity and complexity on earth. Dominant vegetation is tall, broad-
leaved evergreen trees (don’t drop leaves at same time). There are five layers in a mature,
undisturbed forest. Species are adapted to the layer they live in. Many of our houseplant species are
from the lower layers. A temperate forest only has 2-3 layers. The five layers are: Ground layer –
Decomposition is very fast. Nutrients are absorbed quickly. It has nutrient-poor, shallow soils. Shrub layer – Plants are 0 to 6 feet tall. This layer is nearly absent in mature forests (because it is too dark),
unless a tree has falle