Population Biology

What is Population Biology? Population Biology asks the question: What factors cause a population to be the size that it is?

Main Idea #1 Given ideal conditions for growth and reproduction, a population of organisms will grow exponentially.

Exponential Growth Curve

Main Idea #2 Most populations go through a series of growth phases, which can be represented by a logistic growth curve.

Logistic Growth Curve carrying capacity

This Growth Curve Has 3 Phases Lag Phase – little initial growth. Rapid Growth Phase Stable Phase – stabilizing factors limit growth

                                                                                                  Figure 35-6

Main Idea #3 Together, all of the limiting factors acting on a population determine how many individuals can be supported.

Limiting Factors Abiotic factors (temperature, humidity, pH, altitude, light/shade, pollution…) Food supply Interspecific Competition Intraspecific Competition Predation Parasitism/Disease

Density-Dependent/Density-Independent Density-dependent limiting factor: factor that limits a population more as population density increases (e.g. food supply, disease) Density-independent limiting factor: factor unrelated to population density that limits a population (e.g. hurricanes, blizzards, ice storms, and droughts)

Main Idea #4 A population usually achieves a steady state when it reaches the carrying capacity of the environment.

Main Idea #5 Humans have increased our own carrying capacity through agricultural and technological developments, but we have only postponed the environmental limits to our population growth.