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BIOL 215 Notes.pdf

Course Code
BIOL 215
Catherine Potvin

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Lecture 13 - OCT 14
Ecology: the study of relationships between organisms and their environments (which includes
biotic and abiotic components).
The aims of Ecology are (to describe) and to understand the distribution, abundance,
and production of organisms in their environment
Ultimate goal is prediction
MacArthur found 5 different species which occupied the same trees.
How were they able to co-exist?
They occupy the same tree, but different parts
They are occupying the same habitat, but different niches, which limits their interactions
Prevents them from competing and allows them to co-exist
Factors that influence where organisms live
Resources, food
Light (photoautotrophs)
Other species, predators
● Water
Temperature (will be focused on)
Temperature affects the metabolic activities of all organisms
All biochemical reactions are catalyzed by enzymes
Enzyme reaction rates are proportional to temperature.
Enzyme Level
acetylcholinesterase is important in neurotransmission
Trout have 2 forms of the enzyme. One which works well in cold
temperaturesand one that works well in warm.
These two forms match the temperature regime that the fish encounters in winter
and summer.
These trout are then restricted to environments where the enzymes are most
Physiological Level
Physiological differences reflect environmental differences and evolutionary
Most species perform best in a narrow range of temperature
Acclimation to Temperature
Physiological changes in response to temperature changes
Organism Level
Temperature is directly related to population growth

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However if the temperature gets too high, it can kill or injure an organism
Laws of Minimums and Tolerance
Law of Minumums states that each species has a minimum requirement for every
factor necessary to its survival and growth
Law of Tolerance states that even factors necessary for survival and growth can be
stressful when present in too great amount.
How does temperature vary in the environment?
Macroclimate is the climate experienced at large spacial and temporal scales (latitudinal
Microclimate is the climat experienced at scaled of kilometers, or meters, or centimeters
Is influenced by factors like altitude, vegetation, soil colour, aspect (south facing
slopes will have grass, while the north ones will have trees)
Habitat Temperature Variation
Temperature vaires widely among and within environments
Habitat vs. Niche
A habitat is the physical place where organisms live, e.g. tropical rainforest, bottom of
Many organisms occupy the same major habitat
Organisms that live in similar habitats do not live in the same place in the habitat - they
occupy unique niches
Phytoplankton live in the same habitat (lake), but they occupy different niches within the
habitat (depth).
Appropriate combination of conditions for a species to thrive.
Physical and biological factors are determine niche
The ecological niche of an organism is the position it fills in its environment, comprising
the conditions under which it is found, the resources it utilizes, and the time it occurs
So we can look at the specific requirements of each species, beginning with one part of
its ecological niche.
By combining different relevant factors and related data of the presence of a species, it
is possible to construct 3D cubes in space to predict where organisms live
This is referred to as the dimensional hypervolume (the niche)
The set of paramaters is infinite, so the parameters must be chosen. Every set is
The availability of niche at a certain habitat varies in time and space - which
influences the abundance and distribution of the species.
Overlap of niche results in conflict.

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Feeding the Niches of Finches
On the a Galapagos island there are three main finches.
They all have different sized beaks to suit the seeds they eat.
The feeding niche can be determine by the beak size.
There is a variability of beak size within each species.
There was a drought that killed 85% of G. fortis, but it didn’t affect all of them that badly
because they occupied different niches. It favored the larger G. fortis.
Spartina anglica
Hybrid species
Unlike parents, it is very tolerant of saline habitats and water-logged soils
Spread rapidly throughout coastal Europe, Australia, China
Distribution predicted by a few physical variables - tide levels, fetch
Fundamental niche is a niche with appropriate conditions that a species might live in
Realized niche is part of the fundamental niche where a species actually live
Lecture 14 - OCT 19
Population Dynamics
Basic demography
1) Basic Demography
A population is a group of organisms of a single species inhabiting a specific area.
Population dynamics studies the “behavior” of populations such as increases and
decreases in population size. Want to predict the growth or reduction.
The two most important aspects of demography are: death and birth.
The simplest case: Nt+1 = PaNt + bNt
○ Nt is the number at the end of a season
○ Pa is the probability of survival to the next season
b is the average number of offspring produced per adult
Two factors important in determining population growth
1) Sex ratio
There is a bottleneck when there are too little females. Males can
reproducde with many, females can only bear a limited number of
2) Age structure
Demography is always female based (very hard to track paternity)
Organisms which reproduce once in a lifetime
Usually have a lot of offspring
Easy to monitor
Corypha: the tailipot palm
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