Population Ecology

• the study of interactions among living organisms and the interactions with their environment
• the study of the environmental factors and evolutionary forces that influence life histories, distribution and abundance of organisms
• the study of the function and structure of populations, communities, and ecosystems

• fundamental unit
• a single living individual of one species
• evolutionary processes work at the individual level

• consists of all individuals of one species found in a defined area
• longer-lived than an individual organism
• have emergent properties (eg, rates, patterns)

parameters are not present at lower levels

all individuals in an area that potentially can mate and produce fertile offspring (biological species concept)

the place or environment in which the individual or species resides

• increases at a linear rate over time (eg, 1, 2, 3, 4, 5...)
• not observed in many populations over time

• the phase in which the population can initially grow at a rapid pace
• in the absence of competitors, disease, weather, preddators
• in the presence of lots of food

• (dt) = change in time
• (dN) = change in population time
• N = initial population size
• r = reproductive rate per individual (growth rate of population)
• ignores immigration and emigration

b - d = r

• b = birth rate
• d = death rate
• ignores immigration and emigration

• r=0 : no growth (b=d), no change in N
• r<0 : negative growth (b<d), decrease in N
• r>0 : positive growth (b>d), increase in N

• population size does not continue to increase exponentially, but it tends to level off after a certain population size has been reached
• limits to growth imposed by environment, some resources becoming limiting

• [rate of change in population size over time] = [rate of per capita population growth]x[population density]x[unutilized capacity for population growth]
• K=carrying capacity (constant, maximal, sustainable population size)
• is an S-shaped, sigmoidal graph

• dN/dt = 0
• growth rate r = 0
• b = d

...level off or fluctuate around a certain size.

factors that limit the exponential growth of a population

... determine the impact of interspecific competition. Both species compete for the same resources.

if the species compete for long enough, the better competitor can drive the other species into extinction locally

...coexist in the same niche (functional role in a community).