Midterm Flashcards
Exponential Growth
No I or E, constant b&d, unlimited resources, no genetic structure, no age or size structure
Limits on Population Growth
Territory, nesting site, food availability
Population density often limits density
Density Dependent
if B and D increase/decrease with population size
disease, predators, biotic factors,
parasites live better with more people around
Density-Independent
When B and D do not depend on population size (N)
ex: floods, temperature, abiotic factors
As resources become limiting, population growth ___
slows and eventually stops
What is the shape of graph w/ population limitations
Sigmoidial (s-shaped)
Describing births with limited resources
b=b0-aN
birthrate = birth rate with unlimited resources - (constant measuring the strength of density dependence)(population size)
so this infers that as the N increases, the b decreases
Describing deaths with limited resources
d=d0+cN
deathrate = death rate w/ unlimited resources + (constant measuring the strength of density dependence)(population size)
Increase N = increase d
Exponential growth is..
density-independent
With limited resources…
density-dependent
birthrates decline & death rates increase w/ N
K, carrying capacity
the maximum possible population size supported by the environment
K=(b0-d0)/(a+c)
Logistic Growth Equation
dN/dt= rN(K-N/K)
If N is small relative to K
= 1, because N becomes 0
As N approches K
will decline towards zero, which means that the population growth rate will also decline.
*does not mean that the population is decreasing
if N=K
the population is the size of the carrying capacity, the population will not change
dN/dt
the change in population over time, aka population growth rate
if N>K
the (K-N)/K will be negative and the population will decline towards K
Per capita growth rate is maximum when..
b-d=r (when N is close to 0)
Logistic model assumptions
- closed population: no I or E
- no genetic structure
- no age or size structure
- continuous growth with no time lags
- constant carrying capacity
Population Fluctuation
# rise and fall over time erratic
Maximum Sustainable Yield
1/2 K, maximum population growth
Exponential growth vs. Logistic growth
(rN) makes many important assumptions, including unlimited resources in an environment. Clearly this is absurd; all species have some limit on growth.
[rN(1-N/K)] includes this limit, or environmental carrying capacity (K), as a simple modification of the exponential model.
Population Regulation
HAS to be density-dependent
Competition Theory
- same species or w/ individuals
Amensalism or competition
Amensalism
- & 0
one species is harming the other’s success, but not gaining or losing anything themselves
Exploitation Theory
- predation
- herbivory
- mutualism
Commensalism
1: +
2: 0
one species is benefitting while one is not gaining or loosing
Competing
interactions between individuals, over a limited resource, leading to a reduction in the contribution of those individuals to the next generation (fitness)
- Occurs when two species have similar environmental and/or resource requirements or natural enemies
Intraspecific competition
between individuals of the same species
e.g. territoriality, fighting over reproductive females
Interspecific competition
between individuals of different species
e.g. different pollinator species competing for nectar within the same flowers
How do competing individuals interact?
Directly and indirectly
Interference Competition
individuals interact directly and prevent others from gaining access to a resource
Territoriality
Suppress in a direct way the ability of another species to use the same resource. For example, the bird sets up a territory and excludes the other species.
Exploitation Competition
individuals remove a resource needed by others
Light, nitrate
- like trees
Populations depress one another through use of a shared resource, such as food or nutrients.
For example, let’s say a bird species uses the same insect food as another species.
Apparent Competition
individuals affect each other negatively via a shared natural enemy
Shared parasite
Niche
a summary of the range of a species’ biotic and abiotic tolerances and requirements. Only within this range can any individual contribute to future generations
Competitive Exclusion Principle
states that “complete competitors” cannot coexist
Complete competitors
are two species that live in the same place and have exactly the same ecological requirements
What determines where a species is found?
- abiotic constraints
- biotic constraints
- dispersal constraints
Resource Partitioning
When species divide a niche to avoid competition for resources
Different kinds/sizes of food
Feed at different times
Forage in different areas
Exploit the portion of resources
unavailable to othersHow do we model interspecific competition?
Each species will have their own equation for population growth
- Lotka-Volterra
Lotka-Volterra
equations for two competing species
incorporate competition coefficient; alpha and beta
dN1/dt = r1N1(K1-N1-alpha*N2)/K1
Alpha
the effect of one individual of species 2 on the population growth rate of species 1
Beta
the effect of one individual of species 1 on the population growth rate of species 2
Competition Coefficient
alpha or beta - serve to convert the effect of each species into terms of the other
= 1 intra- is equal to interspecific competition
> 1 inter- is greater than intraspecific comp.
Exploitation
the action or fact of treating someone unfairly in order to benefit from their work.
Predators
kill and consume prey - carnivores
Parasitoids
A parasitoid lays her eggs on or in the host. The developing larvae eat and eventually kill the host. Adult parasitoids are free-living insects.
Macroparasites
Parasites obtain sustenance from their host. The parasite often uses the host as both habitat and food. The parasite usually does not kill its host.
