Prof: Dr. Nigel Waltho Mon. & Wed. 10:05am
• Evolutionary Biology – how individuals have evolved and adapted to their environment
through interactions with other individuals, populations and other species.
• Behavioural Ecology – how an individuals behaviours contribute to their survival and
reproductive success and in turn the abundance in that population.
• Physiological ecology – The study of how organisms are physiologically adapted to their
environment and how this limits their distribution patterns.
• Population ecology the study of groups of interbreeding individuals at the same place
at the same time.
Freshwater Biomes: Chapter 24
Water: Is the most dense at 4’C and its least dense as ice. (increases density with salinity)
Layers of Water: (water – chapter 6)
In temperate lakes, in the summer, three layers are present (Figure 24.2c). An upper layer, called
the epilimnion, is warmed by the sun and mixed well by the wind. Below this lies a transition
zone known as the thermocline, where the temperature declines rapidly. Lower still is the
hypolimnion, a cool layer too far below the surface to be much warmed and with low light
Two types of food webs (sun driven)
1 = benticbased macrophytic
2 = pelagicbased microphytic
Cultural Eutrophication: (only takes a couple of years)
Biological Oxygen Demand (BOD)
Dissolved oxygen (DO): the amount of oxygen that occurs in microscopic bubbles of gas mixed
in with the water and that supports aquatic life. Oxygen enters the water directly via diffusion
from the atmosphere, from aquatic plants or algae that release it via photosynthesis, or via
waterfalls and water tumbling over rocks, which traps air.
DO = the same at all levels of the water.
• Lotic (fast moving water) has a higher DO than lentic (slow moving water).
• Also Temperature has an effect, cold water can hold more DO.
Air amount of oxygen 200,000ppm (20%)
cold water 10ppm (less in warm)
(a common water quality test, is testing the BOD
higher bod greater likelihood DO(dissolved oxygen) depleted i.e. how much organic nutrients in the water
higher the bod measure, the more oxygen is required to decompose the material
once all is depleted you are left with an anoxic
anoxic = environment depleted of oxygen ( can be the result of high organic matter being broken
down by bacteri –which use O e.g. near sewage leakage systems)
fish and shellfish are killed when the DO drops below 2 or 3 ppm
if systems go anaerobic (lack of oxygen) the only thing able to survive in water is bacteria
(which adopts a fermentation or anaerobic respiration)
anerobic respiration releases methane (smelly!)
raw sewage BOD = 250ppm
Dissolved Oxygen: Is equal at all levels of the lake.
add nutrients (our sewage, agricultural run off, sediments etc.)
when you add nutrients, phytoplankton, algae will EXPLODE in population
algae floats on top because of photosynthesis advantage, however this provides shade for other
plants and kills them off
NOW, DO 1 = interspecific >intraspecific
cc if<1 = interspecific food webs, photosynthesis(12%) >Biomass >
(bottom up resource availability model)
How much algae that is available controls how many organisms can eat, which determines how
many bigger animals will be available etc. etc.
implies unlimited fishing opportunity
however, fails to explain when high fishing pressure, fish communities collapse, and lakes
EXPLODE with algae! (DUE TO OVERFISHING, MESSES IT UP!)
fishing pressure goes up = removes top predators,
(see lecture slides for formula) collapse of benthic food web
algae don't live long, but reproduce quickly,
when they die they decompose and suck all the oxygen out of the water,
and then everything dies except algae :(
• obviously were missing something….that is, the bottom up resource availability model is
• Brown World with little to no fishing pressure: top down predator prey model
Green or Brown:
demonstrate for benthis substrate Rideau River
assume major grazer is the larval caddisfly.
AQUATIC SYSTEMS ARE BROWN in their natural state
TERESTRIAL SYSTEMS ARE GREEN in their natural state
Nitrogen Limitation Hypothesis:
Two variations: first the plant stress initiation: that when plants are under stresses such as
drought they are more nitrogen heavy and therefore are more appealing to plants.
Second: Plant Vigor Hypothesis: herbivores choose young plants/newly grown parts of plants
because they will be more enriched with fresh nitrogen!
Lecture 9: Chapter 25 – Food Webs & Energy Flow
Autotrophs: harvest sunlight or other chemical energy, and begin at the bottom of the food
chain, providing energy for other animals (primary producers). Insectd and other small animals
that consume primary producers are known as primary consumers.
Organisms that eat primary consumers are secondary consumers, also called carnivores
Organisms that feed on secondary consumers are tertiary consumers, also called secondary
carnivores, and so on. Types of Food Webs:
In connectedness webs, all the known links are drawn and equal importance is attached to each
link (Figure 25.4a). Paine provided the first example of an energy web, where interaction
strengths—based on quantities of food consumed and indicated by the thickness of connecting
Detritus: dead plant and animal material and waste that decomposes and begins life again.
Organisms that assist in the decomposing of such material are called detritivores. (mainly
bacteria and fungi).
Efficiency on Food Webs: (Equations):
• Consumption efficiency is the proportion of production at one trophic level (Prodn − 1)
that is eaten by, or ingested, by the next trophic level (In)
• Assimilation efficiency is the proportion of ingested energy that is assimilated into the
• Production efficiency is defined as the percentage of energy assimilated by an organism
that becomes incorporated into new biomass. It is influenced largely by animal
Complexity of Food Webs:
Linkage density: number of links/ number of species = 40/20 = 2.0
Chain Length: number of different organisms in chain (i.e. lion eats zebra, zebra eats grass, =3
Connectedness: number of links/ Number of total possible links (number of species/
number of links
Not All Species In a Food Web Are Equally Important they are divided into:
A species having a huge effect on a community, out of all proportion to its biomass. (e.g. sea o