Chapter 50: Biomes
Chapter 52: Population Ecology
Definitions :
 Population:
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Deme:
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Population density:
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Dispersion, types of:
Life Tables:
Study of survivorship at different ages of a population, usually by studying a cohort
Cohort:
Using life tables: life tables can be used to generate survivorship curves:

Type I
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Type II
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Type III
Fig. 52.3
Reproductive tables: used to measure fertility at different ages, Fig 52.3
Life History
Reproductive designs/strategies
 Big-bang reproduction/semelparity

iteroparity
Why one design versus the other?
Population Growth
Measuring Population Growth
Change in pop. Size= Births – Deaths
ΔN = B-D
Δt
b = births /year = birth rate
B = births in a given year
B= bN
B= .034 * 500
B= 17
(method to measure expected births)
Use the same for deaths… d = death rate
ΔN = bN -dN
Δt
One othe simplification… b-d represents rate of growth…if positive then
…..if negative then
ΔN = rN
Δt
This is exponential growth, results in a
-shaped curve
FIG 52.8, 52.9
Carrying capacity !!
ΔN= rmax (K-N)
Δt
K
K= carrying capacity, maximum population size environment can support
What happens as population size (N) nears carrying capacity (K)?
Fig 52.10, 52.12
K-selection: density dependent selection, maximizes population size, species that are successful at high
densities. Ex fruit flies
r-selection: density independent, reproductive success greater at low population sizes
Density dependent factors
Density Independent factors
Fig. 52.13,
Attaining equilibrium in a population based on birth and death rates….mathematical models
Fig 52.13
Case I: density-dependent birth rate and death rates
Case II: density dependent birth rate, density independent death rate
Case III: density independent birth rate, density dependent death rate
Assumptions?
Population growth always leads to negative effect, what about too few? Allee effect
Do experimental cases match mathematical models?
What about response time to effects?
Immigration and Emigration?
Growth cycles:
What causes cyclical population cycles?
Boom and bust cycles
Human population growth
Exponential growth…
Noah’s ark?
Age structure diagrams: Fig 52.22
Notes
Ch. 53
Community Ecology
Community: populations in a given area


Species richness
Relative abundance
How are communities built? What factors effect communities?
Two theories FIG 53.1


Individualistic hypothesis: populations grow in same area because they need similar abiotic
requirements…study populations independently
Predicts that each population grows according to its own tolerance to abiotic factors
Interactive hypothesis: communities are populations tied together, act as integrated unit
Predicts that populations dependent on each other will create clusters
Evidence seems to support former in plant communities unless dramatic shift in abiotic factors

Other hypotheses?
Rivet model: analogy…not all rivets are needed on wing but start taking them out?...

Redundancy model: similar to individualistic, species are redundant, if one predator disappears,
others take place. Example: wolves in Yellowstone
How could this be applied to plants? What might happen if an animal disappears? How could this
affect plants?

Scriptural? Our job to understand how God designed communities…what is our job?
Interspecific interactions and Community structure

Competition
Interspecific competition
Competition for limited resources
The Competitive Exclusion principle: SURVIVOR! Outcompete, outsurvive, outresource
Gause: if two species compete for the same resource, one will inevitably outcompete
What determines competitive exclusion? Use of resources...
Ecoligical niche: use of abiotic and biotic factors, the role of an organism in the environment
Apply to competitive exclusion principle…two species cannot coexist if their ________
are the same
Resource partitioning: two species can coexist if one uses slightly different resources
Character displacement: character displacement refers to differences(displacement) in
structures or shapes (characters) examples, Galapagos finches that are usually allopatric
with similar beaks do show differences in beaks on islands where they are both found.
FIG 53.2 and 53.3, 53.4
Also Anole lizards

Predation
Predators, herbivores, parasites
Defenses?
Animal defenses: ?? let’s think
Passive defenses
Active defenses
Unusual defenses
Chemical
Mechanical
Adaptive coloration
Cryptic coloration
Aposematic coloration
Mimicry
Batesian mimicry
Mullerian mimicry
FIG 53.7, 53.8
Plant defenses: strychnine, morphine, nicotine, mescaline, tannins, chemicals
responsible for cinnamon, cloves, peppermint!
Parasites: endoparasites vs ectoparasites

Mutualism: Two species that

Commensalism: hitchhikers
Tropic structure illustrates community dynamics

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
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Feeding relationships between populations
Quaternary consumers
Tertiary consumers
Secondary consumers
Primary consumers
Primary producers (also autotrophs)
Multiple Food chains create food web Fig 53.11
Some animals operate at multiple trophic levels: ex’s?
Observations show that most food chains average five trophic levels
WHAT limits the food chain ? Why only five on average?
Two Hypothesis:
 Energetic hypothesis
Only 10% of energy passed from one level to another (Why?)
100kg of producer→10kg for herbivore→1kg for carnivore
What does this model predict
Approach from mathematical equation, if 100kg increases…
How to test for this prediction?
Fig 53:13

Dynamic stability hypothesis
Food chains are susceptible to disturbances in population numbers, higher levels need to be able to
recover from “wobbles”, if the food chain is longer, larger “wobbles”, harder to recover
Prediction?
How to test?
Compare communities that are
Dominant species and Keystone species
Dominant species have the highest biomass…why dominant? Think back to competition
Keystone species are species that have dramatic effect if removed
Why? Most are predators that influence other populations
How to test? Fig 53: 14 and 15
Studies in Community disturbance
Natural weather events
Examples:
Fig 53: 16,17, 18
Positive or negative?
Succesion:
Development in communities
Primary succession
Secondary succession
Pioneer species: mainly r-selected species
Climax species: mainly K-selected
Soil changes as succession occurs