October 13, 2009
Lecture 13 – Ecological Niche
Ecology – the relationships between organisms and their environments including biological as well as
physical and chemical properties of environment.
Aims of ecology are to describe and understand the distribution, abundance and production of
organisms in their environment. With the ultimate goal of being able to predict changes in environment
and organisms.; when something may occur and why.
Observation: five species of warblers co-existed in the same habitat. Through careful observation it was
noticed that the warblers lived in same tree but did not spend time in the same part of the tree at the
same time. They were living in different niches
The Niche: the environmental factors that influence the growth, survival, and reproduction of a
species. All factors necessary for its existence – when, where and how a species makes its living
Factors influencing where organisms live in their environment include
•Resources (N, P, Ca, etc) food
•Presence/absence/quantity of light (photoautotroph are influenced by light availability)
•Other species and predators
Temperature affects the metabolic activities of all organisms because the biochemistry of cells is
catalyzed by enzyme and their activity is influenced by ambient temperature. Enzyme reaction rates
are proportional to temperature, have higher catalysis rates at higher temperature. At very high
temperature enzymes will degrade and catalysis rate falls off.
Acclimation to temperature – physiological changes in response to temperature changes. For
example atriplex lentriformis (a desert shrub) grown at two temperatures 43/30 and 23/18 (Day/Night).
Temperature dependence of microbial growth on the organism level.
Microclimate is the climate experiences at scales of kilometers, or meters, or centimeters (shade of a
tree on a sunny day). Influenced by many factors including
•altitude (T declines as high increases)
oWhite sand beach reflects all wavelengths of visible light
oBlack sand absorbs all wavelengths of light
•Aspect (north facing vs. south face slope)
•Aquatic vs. terrestrial environment (aquatic environments show less temperature
variation than terrestrial environments)
Habitat – the physical place where organisms live (eg. Tropical rainforest, bottom of a lake, hot spring)
Niche – exist within habitats. Includes physical factors such as temperature and moisture, biological
factors such as resources and predators. The intensity of competition between species suggest the
degree to which their niches overlap.
Law of minimums: states that each species has a minimum requirement for every factor necessary for
its survival and growth. Eg. Minimum T or light
Law of tolerance states that even factors necessary for survival and growth can be stressful when
present in too great an amount
1. The availability of niches within a habitat varies in times and space – which influences the abundance
and distribution of the species
•Feeding niches of finches show a relationship between body size and seed size. The kinds
of seeds eaten by the bird correspond to beak size. During the drought of 77 larger birds
capable of cracking hard seeds survived at a higher rate. Consequently the population was
dominated by larger birds at the end of the drought.
2. New species (invasive species, or as a result of speciation) can spread rapidly within a habitat as they
occupy their niche. Eg. Zebra mussel (bivalve) in North America
•spartina anglica is a hybrid species that arose around 1960s. unlike its parents it’s able
to tolerate saline habitats and water-logged soils. Hybrid species spread rapidly throughout
coastal Europe, Australia and China (where it was planted to stabilize mudflats).
Fundamental niche: the physical conditions under which a species might live, in absence of
interactions with other species (generally only considers abiotic factors, temperature, moisture…)
Realized Niche is the part of the fundamental niche that an organism actually occupies. Limited by
biotic interactions such as competition, predation, disease and parasitism
chthamalus and balanus are barnalces that grow in the intertidal regions on rocky shores. They produce
larvae which settle on the rocks. The larvae grow into adults. Realized niche of chthamalus was much
smaller than that of balanus because balanus is able to displace the fundamental niche of chtamalus.
Measurement of niche breadth -???
Competitive exclusion principle: two species with identical niches cannot coexist indefinitely.
October 20, 2009
Lecture 14 – Population Distribution, Abundance and Growth
Required reading: Molles p. 302-321/p. 266-268
Ecosystem: the grouping of all populations of all species and the physical environment they inhabit
Population a group of organisms of a single species inhabiting a specific area
Three main characteristics:
1. Distribution – the size shape and location of the area occupied by a population
2. Density – individuals per unit surface area
Large-scale patterns of distribution
Limits of population distribution
1. Species have different methods of dispersal across landscape
2. Factors allowing growth and establishment in species upon reaching a new location
•Climate (temperature and moisture)
•Physical factors (wave action, desiccation)
Ex. Tiger Beetle Cincindela longilabris
•The tiger beetle lives at higher latitudes and elevations than most other species. It is a widespread
species with many populations that span over a large geographic range, but always found in
mountains (cold climate). A factor that promotes growth and establishment of the beetle in cold
climates is an evolved physiological trait, a high metabolic rate. This demonstrates how physical
environment limits species distribution
Ex. Kangaroo distributions and climate
•Relationship between climate, moisture and distribution is demonstrated by the distribution of
three kangaroo species in Australia. The Eastern Gray Kangaroo inhabits the eastern 1/3 of the
continent (wet climate). The Western Grey inhabits the southern and western regions (wet and
dry). The Red Kangaroo inhabits the interior (arid and semi arid)
•Limited distributions may not be determined by climate directly. Climate often influences species