3-population ecology Flashcards
population
group of individuals of the same species that live in the same area at the same time
population size
total number of individuals in a popuation
population density
number of individuals per unit area (or volume)
how to choose which sampling technique
organism DOESN’t move? –> QUADRAT SAMPLING
organism DOES move? –> Mark-recapture techniques
Mark-recapture
visit 1
- capture indivduals
- count and mark them (M)
- release them
give marked individuals time to spread out…
visit 2
- capture individuals (n)
- some will be marked (m)
- some will be unmarked
- count them!!!
Lincoln-Peterson method of mark-recapture estimation VARIABLE MEANINGS
M = number of individuals marks on the first visit
n = number of individuals captured on 2nd visit
m = number of individuals captured during second visit that were marked
assumptions of the Lincoln-Peterson method
-
the population is closed
- N does not change between sampling periods
- no births, deaths, or movement of individuals in/out of the population
-
individuals do not differ in their probability of being caught
- marking does not affect probability of being caught
- individuals do not lose marks between sampling periods
Calculating population size at different time points VARIABLE MEANINGS
Nt = population size (N) at time t
Nt+1 = population size (N) at time t+1
D = number of individuals that die between t and t+1
B = number of individuals that born between t and t+1
per capita
per person/individual
Per capita birth rate (range from 0 to infinity)
b = B/N
Per capita death rate (range from 0 to 1)
d = D/N
r variable meaning
per capita growth rate or intrinsic growth rate of the population
r = b - d
CALCULATING POPULATION GROWTH RATE (r) USING b & d
- if b = d the r = 0 → population size is not changing
- if b > d, then r > 0 → population size is increasing
- if b > d, then r < 0 → population size is decreasing
EXPONENTIAL GROWTH
unrestricted growth of a population that increases at a constant growth rate (r)
looks like a j
- r is density-independent under exponential growth
- r won’t change, no matter how big or small the population gets
- the larger the per capita growth rate (r), the steeper the curve
- the larger a population get the more individuals get added to the population with time
LOGISTIC GROWTH
- A pattern of growth that starts fast, but then slows due to limiting factors
- eventually, the population will stop growing (r=0) once it has reached the environment’s carrying capacity
S-SHAPED CURVE
- r is density-dependent under logistic growth
- r will decrease as the population gets bigger and uses more resources
- formula now incorporates the concept of a carrying capacity into the equation
carrying capacity (K)
maximum population size that the environment/habitat can support at a given time
- birth rates = death rates
- in real life, populations fluctuate around K
- Carrying Capacity (K) for a particular species is not constant
- can change over time
- available space changes
- number of individuals the environment supports
- water availability changes
- available space changes
- also differs between species
- different species have different requirements for survival/reproduction
under what conditions can we realistically expect exponential growth to occur?
- when resources are close to unlimited
- when population sizes are relatively small
- ex:
- few individuals colonize new area with few competitors and plentiful resources
- population is recovering from a bottleneck
DENSITY-INDEPENDENT FACTORS
- Affects per capita growth rates regardless of population size
- often abiotic
- ex: hurricanes, COLD, volcanic eruption
factor is NOT more likely to happen if the population size gets larger
DESNITY-DEPENDENT FACTORS
- effect on per capita growth rates depends on population size
- often biotic
- ex: disease, competition for resources, predation
life history
- refers to the stages it goes through in its lifetime
- birth
- growth
- reproduction
- death
life history traits are just a quantification of this life history!!
- age specific survivorship
- age at first reproduction
- number of offspring (fecundity)
- size of offspring
- sex ratio of offspring
- amount of parental care
- reproductive lifespan
survivorship curves
tells us how the probability of survival changes or not with age
type I survivorship curve
most young survive and live until they are old
type II survivorship curve
survivorship declines steadily with age
type III survivorship curve
most individuals live fast and die young, a few live long and die old
r-selected species
- characterized by exponential growth and sudden crashes
- frequent high mortality prevents populations from reaching K
- evolve traits that make them better at growing quickly and spreading fast
tend to organisms that are adapted to environmentally unstable/unpredictable environments - trade-off: having a high quantity of offspring rather than a high quality of offspring
K-selected species
- predation risk low
- offspring receive good parental care
- time and energy spent on parental care = fewer lifetime offspring, but offspring survivorship is high
- tradeoff: high quantity of offspring for high quality, competitive offspring
- organisms adapted to stable environments, where competition is high
- high survivorship allows populations to reach and remain at K
- over time, populations evolve traits that make them better competitors
- important when resources are limiting!!
