Transcript 1. Ecology Introductory Concepts

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The Nature of Ecology
Ecology is the scientific study of the
interactions between organisms and their
environment that determine their
distribution and abundance
Ecologists employ a variety of techniques to investigate:
• The relationship between a single species and the
environment
• The relationships that exist between individuals of
different species within a community, and also between
them and their environment
• The changes that take place in the abundance,
distribution and activity of species
Ecology is a multidisciplinary science encompassing the
techniques and concepts of physiology, chemistry,
mathematics, physics and biogeography
Temperature, rainfall
and light intensity are
the major environmental
factors in determining
the nature of the biome
High temperatures,
abundant rainfall and
roughly constant day
length throughout the
year produce tropical
rain forests
Tropical Rainforest
Tropical forests are characterised by having the greatest diversity of
species of all world biomes; they occur near the equator with high
temperatures and abundant rainfall and roughly constant
day length throughout the year
Savannah
Savannahs are tropical grasslands with scattered or clumped trees;
the climate is tropical semi-humid, with a rainy season in the
summer and a long dry season during the winter months
Deserts
High daytime temperatures and light intensity, little rainfall
and strong winds characterise the deserts – the harshest
environments within the biosphere; organisms colonising these
areas are specialised to withstand the xerophytic conditions
Tundra
Arctic tundra is located in the northern hemisphere, encircling the
north pole and extending south to the coniferous forests of the taiga
Characteristics of the tundra are a cold climate, low biotic diversity
and simple vegetation structure
Ecosystem Structure
An ecosystem is a natural unit which
consists of several habitats and their
communities; it thus consists of both
abiotic and biotic components and
encompasses all their interactions
The habitat of an organism is its place of residence; this is
where it lives, such as at the bottom of a lake, in a cave or
within a tree hole
A population is a group of individuals of the same species which
occupy a particular habitat
A community is a collection of different populations which occur
together in both space and time
The environment of organisms is the set of conditions that
surround them and encompasses their abiotic (non-living) and
biotic (living) environments
An organism’s environment may
be subdivided into abiotic
and biotic components
The biotic environment consists of producers,
consumers and decomposers and, biotic factors
include all the interactions that exist between
them such as competition and predation
The abiotic environment
includes light energy,
water availability, pH,
soil characteristics,
temperature, atmospheric
gases, aspect and altitude
The Ecological Niche
The ecological niche of a population is its
role within the community and is defined as
the sum total of all aspects of a population’s
existence, i.e. its habitat, activities and
requirements together with its effects on
both the abiotic and biotic environments
Ecological niches are the outcome of evolution; species acquire a
range of adaptations through natural selection and these
establish the range and boundaries of the
ecological niche for that species
Every organism of a particular species is adapted to survive
within a range of environmental conditions
The range of environmental conditions within which organisms
survive are described as tolerance ranges and include factors
such as temperature, light intensity and rainfall
Niche Overlap and
Competition
When organisms share the same habitat and
have the same functional roles or requirements for
a particular resource, then niche overlap occurs
When the niches of two species overlap, there is competition for
limited resources such that the greater the overlap, the more
intense the competition
In extreme cases, where two species have identical niches,
competition can be so intense that the different species are
unable to coexist and one species may totally out-compete the
other – The Competitive Exclusion Principle
Competition between members of different species (interspecific
competition) is generally less intense than that observed between
members of the same species (intraspecific competition)
Competitive exclusion is often avoided by dividing up
environmental resources, such that each competitor exploits
different portions of the resource or utilises them at different times;
this is described as Resource Partitioning
Chthamalus populations are potentially able
to grow at all levels of the rocky shore
(fundamental niche)
Chthamalus is more tolerant of high temperature
and desiccation than Balanus and is therefore able
to survive the conditions on the upper shore
The upper distribution limits for both species are
largely determined by their tolerance to these
abiotic factors – temperature and desiccation
The lower distribution limit (realised niche) of
Chthamalus is determined by competition for
space with the faster growing Balanus ;
Balanus balanoides dominates the middle
intertidal zone where it outcompetes the
slower growing Chthamalus
Various biotic factors appear to be responsible
for determining the lower distribution limit of
Balanus balanoides