C4.1 Populations and Communities

208-215 + 216-221

C4.1.1 Populations

Group of individuals of same species living/interacting in an area.

Interbreeding, compete for food, coorporate to avoid predation.

C4.1.2 Estimate population size

Estimate, not count

Random sample: blocks per … so find # of stuff

Sampling error: true - estimated value

C4.1.3 Random Quadrat sampling

throw block and count… good to count sessile organisms

SD = degree of variability

C4.1.4 Captur mark release recapture: Lincoln index

For motile organisms:

1. capture fish

2. mark the fish (M)

3. release the fish

4. recapture fish (N) - nr of them marked = (R)

5. calculate lincoln index

Pop size = ^MxN/_R

Assumed: no migration/death/birth/visible non-harmful marks

C4.1.5 Carrying capacity

Maximum pop size that env can support: resources (water, light nutrients, oxygen)

C4.1.6 Negativ feedback control of population size

Fluctuating but never actually in/decrease too far:

Density dep factors: increase w pop size: competition, predation, disease/parasites
Density indep: same effect no matter pop: fire

C4.1.7 Pop growth curves

Positive feedback: reproduction = exponential: new/new niche: resources abundant

Then plateau as carrying capacity reached

C4.1.8 Model sigmoid pop growth

find carrying capacity.

C4.1.9 Communities

Community: all populations living and interacting w each other

C4.1.10 Intraspecific relationships

Intraspecific: relationships between individuals of same species

1. Competition: same ecological niche (light, food, territory, mates…)

2. Cooperation: mutually good: hunt in groups, defend predator, stay tg (warm)

C4.1.11 Interspecific relationships

Interspecific: relationships between different species

1. Herbivory: primary consumer eating primary producers: animal eating plant

2. Predation: kill organism: eat it: animal eat animal

3. Interspec comp: compete for resource; ivy climbing oak for light

4. Mutualism: 2 species benefitting from each other: bees/flower

5. Parasitism: parasite (benefit) live in host (harmed): ticks on animals

6. Pathogenicity: pathogen in host (cause disease):tuberculosis bacteria→diseas

C4.1.12 Mutualism

1. Peas have nodules that protect bacteria from consumers, and provide sugars, the bacteria fixes nitrogen to help plant

2. Orchids give sugar (for photosynthesis) to fungus, fungus supplies nutrients

3. Coral provide protected env close to surf where algae abs light+CO₂, algae provide sugars + O₂ from photosynthesis to coral

C4.1.13 Endemic vs Invasive species

Endemic: occur naturally in area

Alien: introduced outside range by human activity

Invasive: alien but spread rapidly bc no densitydep factors: outcompete endemic

compete for resources

C4.1.14 Test for interspecific competition

Chi-Squared test:

random quadrat sampling → A, B, AB
H₀: distributed independently, H₁: associated
Rejecting null hyp doesnt mean competing, need further investigation

C4.1.15 Chi-Squared test (X²)

Expected = ^{row total x column total}/_{grand total}

In table 1: nr of specie A pres/abs, specie B pres/abs
In table 2: exp nr of: A pres/abs, B pres/abs

Then: observed vs expected table: find X² → (Obs-Exp)²/_Exp → sum of all = X²

Calculated X² vs critical value: df(nr of species - 1), at p=0.05:
if X²>critical value: reject H₀: 95% confident that association between species

C4.1.16 Predator Prey relationships

Cycles with each other:
more prey:more pred→more pred:less prey→less pray:less pred→less pred:more prey

C4.1.17 Top down/Bottum up control of populations

Top-down: higher in food chain effect lower levels: predation
Bottom-up: lower affect higher: nutrient sources

Both can happen, one will be dominant

Food chain: nutrient→producer→herbivores→predators

C4.1.18 Allelopathy

Target metabolic pathway to control population:

Antibiotic: secreted by penicilin and break down cell wall of bacteria:

Allelopathic agents: secreted by plants into soil to kill other plants (invasive species)