Chapter 6 Population Biology APES 2009-2010

Outline Dynamics of Population Growth Factors that Increase or Decrease Populations Factors that Regulate Population Growth Conservation Biology

Lecture #1 Dynamics of Population Growth Population - all the members of a single species living in a specific area at the same time dN/dt = rN The change in the number of individuals (dN) per change in time (dt) equals the rate of growth (r) times the number of individuals in the population (N). r is often called the intrinsic capacity for increase.

Population balance   For an ecosystem to be stable over a long period of time, the population must remain more or less constant in size and geographic distribution. Population balance occurs when there is an equilibrium between births and deaths Problems can occur if a population is out of balance. Example: not enough resources for all

Biotic Potential Biotic Potential- The number of offspring that a species may produce under ideal conditions Biotic potential varies among the different species. Examples: Mice = can breed every 6 weeks. Some plants = many millions in a year

(Biotic potential cont) Biotic potential refers to unrestrained biological reproduction. Biological organisms can produce enormous numbers of offspring if their reproduction is unrestrained. Things that limit populations (Constraints) include: Scarcity of resources Competition Predation Disease

To have any effect on the size of future generations the young must survive and reproduce Recruitment - Survival through the early growth stages to become part of the breeding population Survivorship is determined by the percentage of a cohort that survives to a certain age

r and K Selected Species There are differences in biotic potential and recruitment. This brings about two different reproductive strategies. r selected species rely upon a high reproductive rate to overcome the high mortality of offspring with little or no parental care. Example: A clam releases a million eggs in a lifetime. This strategy results in low recruitment. K selected species have few offspring but more parental care. Example: An elephant reproduces every 4 or 5 years. This strategy results in high recruitment

Reproductive Strategies

Exponential Growth If the biotic potential of a species is realized, the resulting growth would be exponential. Exponential Growth - growth at a constant rate of increase per unit time (geometric) ; has no limit Number of individuals added to a population at the beginning of exponential growth is relatively small. But numbers increase quickly because a % increase leads to a much larger increase as the population grows. J curve when the equation is graphed Exponential growth is a simple, idealized model. In the real world there are limits to growth.

Carrying Capacity Carrying capacity - limit of sustainability that an environment has in relation to the size of a species population Overshoot - population exceeds the carrying capacity of the environment and death rates rise as resources become scarce Population crash - growth becomes negative and the population decreases suddenly Boom and bust - population undergoes repeated cycles of overshooting followed by crashing

Growth to a Stable Population Logistic Growth - growth rates regulated by internal and external factors until coming into equilibrium with environmental resources dN/dt = r N (1 - N/K) Terms have the same definitions as previous slide, with K added to indicate carrying capacity. Growth rate slows as population approaches carrying capacity. S curve when the equation is graphed

Logistic Growth Curve or S Curve