Topic 16 Flashcards
What factors influence population growth (b, d, r) in crowded populations (at high N) ?
- intraspecific competition increases
- predator density increases
- parasite density
- disease
Density dependence may reduce growth, survival and reproduction of individuals in a population thereby affecting….
population growth through b and d (r) with increased crowding
Logistic model of population growth primary underlying assumption
factors limiting population growth exert stronger effects on b and d as a population grows
Under the logistic model of population growth K represents a..
stable equilibrium around which the population size fluctuates
Degree of fluctuation often due to..
time delay in feeling the effects of increased population density
Density independent factors
environmental (temp, precipitation). influence b and d and reproduction rates
If changing environmental conditions exceed an organisms range of tolerance then..
growth, reproduction, maturation, survival and dispersal can all be altered
Spruce bud work outbreaks are connected to
long periods of drought, outbreaks end when moist conditions return and are beyond their tolerances
Density dependent factors tend to bring populations under..
control and maintain their size close to K (cause of biotic factors, competition)
Density independent factors tend to reduce populations far below..
K and initiate periods of population recovery (abiotic factors, temp, environment)
The relative importance of DD and DI factors will depend on
- intensity and frequency of environmental fluctuations
- life history characteristics of population in question
DD factors likely interact with DI factors in a
complex way to cause variable patterns in population size
Sustainability
matching quantities of harvest rate to rate of population growth (supply rate = demand rate)
We want to harvest the max number of individuals from a population without …
diminishing ability of the population to regenerate over the long term
Yield
number of individuals of a species harvested per unit time
Sustainable yield objective
ensure a similar yield at each harvest
Assumptions of sustainability
species or resources are renewable (resupplied)
If non renewable
harvest if never sustainable. ex: mineral resources (copper) can be recycled efficiency reduces harvest rate (demand)
If renewable at slow rate
harvest is non sustainable. ex: fossil fuels, supply rate is around 0 at the rate of human consumption
If renewable at fast rate
to be sustainable the demand rate should not exceed the supply rate, otherwise the population will decline
Maximum sustainable yield (MSY)
largest average harvest/yield that can be continuously taken from a population without causing a population decline (supply > or = harvest/yield)
MSY goal
maximize economic gains. harvest rate = replacement rate
We can to keep N where..
r is the highest
The rate of change of a population is max at
K/2
Intermediate population sizes have the..
greatest growth rate (or ability to produce the max number of harvestable individuals)
Opitimist harvest (economic gains) by …
harvesting enough individuals to keep the population at intermediate sizes (K/2)
Problems w MSY
- hard to quantify N at given time
- environmental conditions constantly change K, so difficult to quantify K/2
- density independent factors can be unpredictable causing high mortality and reducing N
- age structure of pop. chance. r depend on age specific b and d rates
- failure to incorporate economics
Examples of problems a MSY
fisheries. if reduce harvest fishers cannot maintain payments, wages of crew = unemployment. politicians will lose votes as fishers lose livelihood.
