Community Ecology and Population Dynamics
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Community Ecology
The study of ecological interactions between individuals of two or more species.;interactions and impact on species
Competition - - (both negative impact)
exploitative + - (one species being exploited)
Competition - - (both negative impact)
exploitative + - (one species being exploited)
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Mutualism + + (both species benefit);Intraspecific Competition
Competition within SAME species
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**Must directly encounter each other and the same resource;Interspecific Competition
Competition among DIFFERENT species
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Must be the same resource (international species);Interference competition
individuals interact directly with one another by physical force or intimidation
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**However, they must interact directly and the exact same resource;Exploitation Competition
- Species using the same competitive resource
- Species that is more efficient at getting that resource wins
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**Indirect interaction, DO not encounter, only over the shared resource (populations depress one another through use of a shared resource;Competitive Exclusion
The principle that when two species are too similar in their resource use, they cannot coexist
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-weaker competitior experiences a *Niche Shift*, having to change and adapt their foraging strategy;stable coexistence (equilibrium)
- A stable equilibrium point where two species coexist at unchanging densities.
- Coexistence is possible
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***Intraspecific competition is stronger than interspecific competition;Unstable coexistence (equilibrium)
An outcome of a competition model that leads to an unstable equilibrium that contains both species, because the equilibrium is unstable,
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*with eventual competitive exclusion;Niche
- the total range of Environmental conditions under which an organism can survive & reproduce
- *Shapes population distribution and abundance
- * Resources it can tolerate and utilize
- (Principle of allocation: organism has limited energy to devote to life functions (survival, growth, reproduction))
- N(t) = N(t-1) + B + I - D - E
- N(t): population at present
- N(t-1): population at time point in past
- B:births
- I: immigration(influx)
- D: deaths
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E: emmigration(exiting)
Population dynamics equation;Environments where resources are abundant, density is low, and limiting factors (like predators, disease, or competition) are absent
N(t) = N(0)*λ^t
N(t):future individuals at time t
N(0): initial individuals
t = years from N(0)
λ: finite per capita growth rate (1+b-d)(rates)
λ=1 staying the same
λ>1 growth (greater = greater)
N(t) = N(0)*λ^t
N(t):future individuals at time t
N(0): initial individuals
t = years from N(0)
λ: finite per capita growth rate (1+b-d)(rates)
λ=1 staying the same
λ>1 growth (greater = greater)
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λ<1 declining (less = less);Geometric growth
- *looks at time in discrete chunks, good for populations that have defined breeding periods or seasons. (closed pop, No resource or demographic (all population considered to reproduce) limitations)
- N(t)=N(0)e^rt
- N(t): future individuals
- N(0) starting pop
- t = years from N(0)
- r: per capita rate of growth (b-d)
- r= 0 stays the same
- r>0 growth (greater = greater)
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r<0 decline (less = less);Logistic Growth
looks at time as continuous, no demographic limitation, births and deaths are constant
dN/dt = rmax*N*((K-N)/K)
N is constantly changing
dN/dt = rmax*N*((K-N)/K)
N is constantly changing
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growth rate is highest at k/2 (inflection point);Carrying capacity
number of individuals that the environment can sustain (K) (growth rate is highest at k/2(inflection point) is constant in logistic growth model however in real life can change with habitat loss, disease, natural disasters.
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**important because the carrying capacity (K) is the "brakes" of the logistic growth model equation.;Survivorship Curves
Type I (whale, humans): low early mortality aka high juvenile survival rate until the end of their lifespan
Type II (bird): typically expreienceing contant mortality rate (downward line)
Type II (bird): typically expreienceing contant mortality rate (downward line)
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Type III (bug): high offspring production and high juvenile mortality rate, followed by a low adult death rate and higher survival rate.;Life table values
- Age (x)
- Survivorship (lx) = always divide current by first stage 777/777
- Birth rate (mx)
- (lxmx is pretty intuitive (multiply) same for xlxmx)
- get the sum for these values to determine:
- R0 = (Esum lxmx) Net reproductive rate
- T = (Esum xlxmx)/R0 Generation time( avg time individual gives birth)
- r = (ln(R0))/T
- *r > 0 growing (greater = greater)
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** r < 0 declining (less = less);Lotka-Volterra Model
- allows us to model interspecific competition & look at chances for coexistence or competitive exclusion (based on logistic)
- alpha is species 2 on 1, beta is 1 on 2
- dN1/dt = r1N1 ((K1-N1-αN2)/K1) (reverse numbers for other)
- *α > 1, Interspecific competition effect is stronger
- *β < 1, intraspecific competition effect is stronger
- N1(x) N2(y)
- (k1,0) (0,k2)
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(0,k1/α) (k2/β);Possible long-term outcomes of interspecific competition
1. Extinction - species completely dies out
2. Exclusion - weaker competitor experiences niche shift
2. Exclusion - weaker competitor experiences niche shift
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3. Evolution - resouce partition & characteristic displacement;predators
kill & consume other organisms;parasites
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**Influence the distribution, abundance, & structure of prey populations;Plant physical defenses against herbavores
-Thorns
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-High silica causes teeth to wear down (grass);Predator Lotka-Volterra Model
Assumes predator growth rate is determined by rate of conversion of food into offspring minus mortality rate of parasite or predator (based on exponential growth (no K))
dNe/dt = cfNpNe-dNe
c & f are constant Ne is exploiter, Np is prey (dNe is individuals removed)
dNe/dt = cfNpNe-dNe
c & f are constant Ne is exploiter, Np is prey (dNe is individuals removed)
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** Changes in one population immediately result in responce by the other, Increased predation = more predators; more predators lead to higher exploitation rate, eventually reducing host(prey) population;Outcomes and patterns of Lotka-volterra model of predation
- 1. Predator goes extinct
- prey grows exponentially*
- 2. prey goes extinct
- predator also goes extinct*
- 3. both have stable populations
- damped oscillations
- 4. stable predator/prey oscillations
- damped oscillations amplitude decreasing over time
- exploding oscillations, amplitude increasing over time
- *extinction depends who hits rock bottom first(predator or prey)
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Stabilizing factors produce damped oscillations (ex. prey refuges, think paramecium tube where the prey could hide);Primary defense strategy
Camouflage(crypsis), avoiding the prey altogether;secodary defense strategy
-Make their own foods, using inorganic sources of carbon & energy
Photosynthetic - use co2 as carbon source & sunlight energy
-Make their own foods, using inorganic sources of carbon & energy
Photosynthetic - use co2 as carbon source & sunlight energy
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Chemosynthetic - use organic molecules as source of carbon & inorganic molecules as source of energy;Hetertrophs
Organisms that depend on other organisms for their food.
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-Herbivores, carnivores, detritivores;Red queen hypothesis
The evolutionary hypothesis that all species must constantly evolve in order to maintain their fitness in the face of a changing environment full of other evolving species.;Allele effect
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-fits social dynamics of animals (strength in numbers);coevolution
Evolution by natural selection through reciprocal selective pressures between two or more closely interacting species.
Example: predators speed vs prey camoflague a sort of evolutionary arms race that pressures the other trait to be naturally selected against.;
Example: predators speed vs prey camoflague a sort of evolutionary arms race that pressures the other trait to be naturally selected against.;
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