Populations Dynamics

1. Populations Dynamics Chapter 36

3. I. Environmental Factors • Living organisms are influenced by a wide range of environmental factors. These can be two types: • Abiotic factors – nonliving environmental factors (water condition, air quality, salinity, temperature, soil content, etc.) • Biotic factors – living organisms that interact with the organism we are studying (prey, predators, infectious agents etc.)

4. II. Population ecology • Population ecology is the study of how and why populations change. Also studies population numbers, where you find the studied population and how many organisms live in it, how/why it increases/decreases in numbers. • Population – a group of individuals of the same species that live in the same general area (same resources, same environmental influences, common breeding, social interactions)

5. III. Population Growth • The number of individuals comprising a population may fluctuate over time. These changes make populations dynamic. • A population in equilibrium have about the same individuals from one generation to the next. • Factors that can change the number of individuals in a population: • Birth (B) • Death (D) • Immigration (I) • Emigration (E)

7. IV. Population Structure (density, dispersion and age structure) • Population Density – the number of individuals of a species per unit area or volume. • Measuring population density: • By counting • Sampling techniques (http://www.biologycorner.com/flash/mark_recap.swf ) • Patterns of distribution • Clumped • Uniform • Random (rare, temporary)

9. B. Age structure is determined by • Life tables – Determine the average lifespan to study the dynamics of population growth. http://www.ssa.gov/OACT/STATS/table4c6.html • Suvivorship Curves – they plot the # of individuals alive in each age • Type I – produce few offspring, take care of their young, many survive into maturity • Type III – high death rates for the very young, mature individuals survive longer, usually involves very large # of offspring with little or no parent care. • Type II – intermediate, more constant mortality over the entire lifespan

11. V. The Patterns of Growth • The Exponential Growth Model • The rate of population increases exponentially under ideal conditions (high birth rate, low death rate). • The population multiplies by a constant factor during each time interval. • Endless resources • J-shaped curve • Colonizing populations • http://www.pbs.org/wgbh/nova/earth/global-population-growth.html

13. During exponential growth, all members of the population will have the maximum capacity of reproduction. B) Carrying Capacity – Logistic Growth • Environmental factors limit population growth. • With limiting factors included growth curve resembles a logistic growth curve (S-shaped curve)

14. K : Carrying capacity – the maximum population size that a particular environment can support. It’s value depends on the species and environmental resources. • Ultimately, a population would stabilize on the carrying capacity (K) – birth rate equals death rate.

15. C) Factors Limiting Population Growth • Density-dependent factors – factors that have greater effect when the population density is higher. • Competition for food, territory • Health of organisms • Predation • Parasites • Physiological factors (reproduction, growth, hormonal changes)

16. Density-independent factors – Regardless of population density, these factors affect individuals to the same extent. • Weather conditions • Acidity • Salinity • Fires • Catastrophies • Boom-and-bust cycles – the number of individuals within the population seems to show a cyclic change. • Predator/prey relationships • Changing food supply Figures 36.5C and 36.6 on page 733.

17. VI. Age Structure Diagrams • Human population can also be described by age structure diagrams. These diagrams are frequently dependent on the economy and social state of the country that they are measured in.