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BIOLOGY 1M03 Final: Bio 1M03 Ecology Notes

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Jon Stone
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Bio 1M03: Ecology Notes
Definition of Ecology: The study of the factors determining the distribution and abundance of
organisms; flows of energy and nutrients through biological systems
- Tells you certain consequences of actions, not what you should do
Hierarchical Levels of Ecology
- How do individuals interact with each other and their physical environment?
- Salmon migrate from saltwater to freshwater environments to breed
- Interactions among individuals; population growth, extinction
- Important from management point of view (How many salmon will there be at any given time?)
- How do species interact and what are the consequences?
- Interactions among different species (Salmon are prey as well as predators)
- What maintains biodiversity (also used in epidemic models)
- How do energy and nutrients cycle through the environment?
- Tracking energy and nutrient flows (salmon dies and then decomposes, releasing nutrients used by
bacteria etc.)
- Allochthonous inputs: moving nutrients into an environment from someplace else
Limiting factors in Ecosystems
Bottom up factors: Things that organisms need to grow
- How fast can they produce biomass
- Needed for biochemical reactions, especially photosynthesis
- Light (photons)
- Nutrients (especially nitrogen, phosphorus, iron)
- Water
- Temperature
Liebig's law of the minimum: A general law that states the most limited factor is what will determine
how much organisms can grow
Top-down Factors: Regulate the rate of loss, rather than the rate of production
- Influence of predators (especially on grazers), fire
- How fast is biomass being taken away
Aquatic Ecosystems
- Important factors include temperature, nutrients, light, wind (mixes the top and bottom)
- Top layers of water columns tend to be warmer and brighter; less available nutrients because they
are used up by top organisms; high in oxygen
- Bottom layer is darker and cold but is nutrient rich; low in oxygen
Oxygen levels are an indication of plant growth (because they produce it)
- There are different limiting factors in different parts of the ocean
- When these layers get mixed, there is lots of production; therefore, wind is good
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Freshwater Ecosystems (Mostly Lakes)
Photic Zone: Top layer; temperature of top fluctuates between warm and cold
Aphotic Zone: Bottom layer;
Seasonal Overturning/Stratification: Since warm water is less dense, when the top layer changes
temperature, the entire lake mixes (typically happens twice a year); this mixes nutrients
- More shallow waters experience more fluctuation
- Upwelling can also be bad; (overwhelming plant production leads to lake covered with green slime)
Marine Ecosystems
- Don't change temperature enough for the entire ocean to overturn
El Niño and El Nina: seasonal currents that mix the waters
Upwelling: The movement of bottom water up to the surface; also moves nutrients up to the surface
- Heavily influenced by iron; lack of iron limits marine productivity (geo-engineering)
Benthic Ecosystems
- Stuff happening on the very bottom of an ocean; deep ocean; ocean floor
- No photosynthesis can occur because there is no light
- All food comes from somewhere else
Donor-controlled: Organisms wait for resources that come (dead whale falls)
- There are organisms that specialize in decomposing dead whales
Chemoautotrophic: Can synthesize organic compounds from energy in environment chemically
(typically sulphur reducers)
- Cold seeps: Cold areas that are sulphur rich
- Hot smokers: Geothermally active areas rich in sulphur
Terrestrial Biomes
Biome: A large scale biological community
- Differences between terrestrial biomes are mostly dependent on water and temperature
- Light isn't one of the main ones because water and temperature are more limiting
Holdridge Zones: A different way of categorizing biomes
Evapotranspiration: The process by which plants are evaporating water off the surface of their leaves
and pulling water out of the ground;
Potential Evapotranspiration: A measure of how much plants could pull out of the ground and
evaporate; can be calculated using water and temperature
- Too dry = no water available to be evaporated
- Too cold = water cannot evaporate
- Really cold or dry = low potential
- Any place that is really dry looks like a desert
(not much variation)
- Any place that looks really cold look like a
tundra (not much variation)
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Behaviour Ecology
Behaviour (definition)
- Any way that an organism changes in response to a stimulus
- Overlaps with phenotypic plasticity (genome doesn't change but gene expression changes)
- Organisms can change gene expression or also change neuronal activity which is a rapid change (for
organisms with nervous systems)
- Plants take up less root space when sharing with relatives (cooperate)
Proximate vs. Ultimate Causation
Proximate causes: Describing the immediate causes of something happening (how?)
Ultimate causes: The far removed reason (why?)
Genetics of Behaviour (Fruit Flies)
Rover: A version of a fruit fly gene that causes larvae to craw all over for food
Sitter: A version of a fruit fly gene that causes larvae to stay in a food patch
- Rovers are more fit in high population density environments
- Sitters are more fit in low population density environments
- Same gene also exists in honeybees, other insects, and adult fruit flies
Foraging Ecology
- How do organisms find food and decide what to eat?
Foragers: Predators, herbivores, frugivorous, netarivores...
Handling Time: How long does it take to deal with a piece of food before being able to get more food;
opening nuts, digesting, chasing prey etc.
Search Time: How long does it take to find food; rare food that is hard to process might not be worth
the search
Food Choice
- Food preference defined relative to availability
- An organism eating an abundant amount of food doesn't necessarily like the food, it depends on
what is available
- Humans might choose to eat a lot of junk food because it used to be good for us
- Other humans might eat junk food because they have low income and have no choice
Foraging Trade-Offs
- Energetic return is sometimes measured (fitness is hard to measure)
- Bee-eaters only go farther distances for richer resources
Ideal Free Distribution: If there are multiple food patches, some better than others, and organisms
can choose whichever one they want to go to, organisms will sort themselves out proportionate to
the amount of resources available
- Resources are divided efficiently
Rate Maximization: Maximize energy gain per unit time
- Energy gain depends on size, nutritional content, lack of toxins etc.
- Time spent depends on search time and handling time
Model Predictions: Pick prey with maximal energy/time
- Be choosy when preferred prey are abundant (opportunity cost of handling crappy prey); no point
wasting time for the less abundant prey
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