Topic 16 -Population Regulation Flashcards
Density-Dependence
What factors influence population growth (b, d, r) in crowded populations at high N?
Intraspecific competition
Predator density increases (higher risk of predation)
Parasite density (higher risk of parasitism)
Disease (higher rate of disease perpetuation)
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
primarily underlying assumption:
factors limiting population growth exert stronger effects on b and d as population grows (population growth is density-dependent)
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-independence
influences other than density can act on a population altering growth and reproduction
density-independent factors
environmental: temp, precipitation, and natural disasters
influences b and d rates and even reproduction within a population
if changing environmental conditions exceed an organisms range of tolerances
growth, reproduction, maturation, survival and dispersal can all be changed and altered
density dependent factors tend to bring population sizes under control and maintain their size close to
k, caused by biotic factors (competition, predator and prey interaction)
density independent factors tend to reduce populations….
far below k and initiate periods of population recovery, caused by abiotic factors (temperature)
the relative importance of D-D and D-I factors will depend on
intensity and frequency of environmental factors
life history characteristics of the population
frequent and extreme environmental fluctuations
r selected
mechanism of regulation?
density independent
infrequent and mild environmental fluctuations
k-selected
mechanism of regulation?
density dependent
all populations undergo some type of
regulation, and is not necessarily occurring all the time, D-D and D-I likely interact to in a complex way to cause variable patterns in population size
Sustainability
matching quantities of harvest rate to the rate of population growth (supply rate = demand rate)
want to harvest the maximum number of individuals from a population without diminishing the ability of the population to regenerate over the long-term
yield
number of individuals of a species harvested per unit time
objective: ensure a similar yield at each harvest -sustainable yield
Maximum Sustainable Yield
largest average harvest (or yield) that can be continuously taken from a population without causing a population decline (supply > or = harvest/ yield)
Goal for Maximum sustainable yield
maximize economic gains
maintain maximum population growth rate (or replacement rate) of the harvested population
harvest rate = replacement rate
how do we quantify MSY
the rate of change of a population is maximum at k/2
intermediate population sizes have the greatest growth rate (or ability to produce the maximum number of harvestable individuals)
problems with Maximum sustainable yield
Hard to quantify N at any given time
Environmental conditions constantly change k, making it difficult to quantify k/2
Density-independent factors can be unpredictable, causing high mortality and reducing N
Age structure of a populations change -r (growth rates) depend on age specific b and d rates
Failure to incorporate economics -strong pressure to maintain harvest at previous levels to maintain payments on infrastructure
if reduced harvest….
fishers cannot maintain payments, wages of crew which leads to unemployment and collapsed industry
politicians lose votes as fishers lose livelihood
reducing harvest rates meets strong oppositions
