Population Ecology

		Varied life Histories 
•	The life history of a species consists of growth, dispersal, and reproductive stages. Many organisms have complex life histories. 
•	A population consists of all the individuals of a species within a given area. 
•	Trade-offs inevitably exists between number and size of offspring, between number of offspring and parental care, between survival and reproduction, and between growth and reproduction. 
•	Reproductive value is the average number of offspring that remain to be born to individuals of a particular age. Reproductive value rises to a peak when individuals first begin to reproduce and then declines to zero after reproduction ceases. 
		Population Structure: Patterns in Space 
•	The number of individuals of a species per unit of area (or volume) is its population density. Dense populations often exert strong influences on populations of other species. 
•	Its age distribution reveals much about the recent history of births and deaths in a population. The timing of births and deaths may influence age distributions for many years. 
		
		Population Dynamics: Changes over Time 
•	Births, deaths, immigration, and emigration drive changes in population density and distribution. 
•	Life tables help us visualize patterns of births and deaths in a population. 
•	Graphs of survivorship in relation to age show when individuals survive well and when they do not. 
		Exponential Population Growth 
•	All populations have the potential to grow exponentially when they colonize suitable environments. 
		Population Growth in limited Environments 
•	No population can maintain exponential growth for very long because environmental limitations cause birth rates to drop and death rates to rise. 
•	The number of individuals of a particular species that an environment can support called the carrying capacity is determined by the availability of resources and by disease and predators. 
•	A population in a constant but limited environment at first grows rapidly; but growth rates decrease as the carrying capacity is approached. 
•	Metapopulation dynamics are determined by "births" (colonizations) and "deaths" (extinctions) of local subpopulations. Immigrants may prevent declining subpopulations from becoming extinct, a process known as the rescue effect. 

		Population Regulation 
•	Regulation of a population by changes in per capita birth or death rates in response to density is said to be density- dependent. 
•	If per capita birth and death rates are unrelated to a population's density, population regulation is said to be density independent. 
•	The abundance of a species is determined by the combined effects of all density-dependent and density-independent factors affecting it. 
•	Populations of many organisms are below carrying capacity most of the time because they are recovering from disturbances. 
•	Population densities of most species are high near the center of the species' range and decline toward the periphery. 
		Humans Manage Populations 
•	Humans use the principles of population dynamics to control and manage populations of desirable and undesirable species. Nevertheless, many populations have been overexploited. 
•	Earth's carrying capacity for humans has been increased several times by technological developments. Whether the current human population exceeds Earth's carrying capacity is hotly debated.