Population Principles Chapter 3

Population Characteristics Population - Group of individuals of the same species inhabiting the same area simultaneously. (6.4 Billion – 2004) Natality and Mortality Natality - Number of individuals added through reproduction. Birth Rate (Humans Born / 1,000) Mortality - Number of individuals removed via death. Death Rate (Humans Died / 1,000)

Figure 7.1

Population Characteristics Population Growth Rate - Birthrate minus the death rate. Often expressed as a percentage of the total population. (Geometrically – Population)(Arithmetically – Food Supply) Survivorship Curve - Shows proportion of individuals likely to survive to each age. High mortality in young. Mortality equitable among age classes. Mortality high only in old age.

Survivorship Curve (Fig.7.2)

Sex Ratio and Age Distribution Sex Ratio - Age Distribution Sex Ratio - Relative number of males and females in a population. Females determine the number of offspring produced in sexually reproducing populations. Age Distribution - Number of individuals of each age in the population. Greatly influences population growth rate.

Age Distribution in Human Populations (Fig.7.3)

Population Density and Spatial Distribution Population Density - Number of individuals per unit area. High population may lead to increased competition for resources. Dispersal - Movement of individuals from densely populated locations to new areas. Emigration - Movement from an area. Immigration - Movement into an area.

Population Growth Curve Biotic Potential - Inherent reproductive capacity. (Biological ability to produce offspring) Generally, biotic potential is much above replacement level. Natural tendency for increase. All living populations follow an exponential growth curve.

Exponential Growth Curve Lag Phase - First portion of the curve; slow population growth. Exponential Growth Phase (Log Phase)- More organisms reproducing causing accelerated growth; continues as long as birth rate exceeds death rate. *Currently* Stable Equilibrium Phase - Death rate and birth rate equilibrate; population stops growing.

Biotic Potential (Fig.7.4)

Typical Population Growth Curve (Fig.7.5)

Carrying Capacity Carrying Capacity - Number of individuals of a species that can be indefinitely sustained in a given area without harming the habitat.

Environmental Resistance Environmental Resistance - Any factor (limiting factor) in the environment limiting carrying capacity. Four main factors: Raw Material Availability Energy Availability Waste Accumulation and Disposal Organism Interactions Disease, Predation, and Space

Carrying Capacity (Fig.7.6)

Bacterial Growth Curve (Fig.7.7)

Fig. p.138

Reproductive Strategies and Population Fluctuations Not all species reach a stable carrying capacity. Species can be broadly lumped into two categories: K-strategists r-strategists

K - Strategists Large organisms Long-lived Produce few offspring Provide substantial parental care Populations typically stabilize at a carrying capacity. Usually occupy relatively stable environments. Reproductive strategy is to invest in a few, quality offspring.

K - Strategists Controlled by density-dependent limiting factors. Factors that become more severe as the size of the population increases. Diseases Deer - Lions - Swans

r - Strategists Small organisms Short-lived Produce many offspring Little if any parental care Usually do not reach carrying capacity (boom-bust cycles). Exploit unstable environments. Reproductive strategy is to produce large numbers of offspring to overcome high mortality.

r - Strategists Controlled by density-independent limiting factors. Population size is irrelevant to the limiting factor. Weather Conditions Grasshoppers - Gypsy Moths - Mice

Population Cycles (Fig.7.8)

Human Population Growth Major reason for increasing human population growth rate is an increase in medical care, and a consequential decrease in death rates.

Historical Human Population Growth (Fig.7.9)

Doubling Time Doubling Time of a Population (years) : 70 / Population Growth Rate (%) ( 70 / 2.0% = 35 years )

Doubling Time for the Human Population (Fig.7.10)

Human Population Growth Interactions Affecting Carrying Capacity Available Raw Materials Available Energy Waste Disposal Interaction With Other Organisms

Social Factors Influence Human Population Humans are social animals who have freedom of choice. People make decisions based on history, social situations, ethical and religious beliefs, and personal desires. Biggest obstacles to controlling human population are not biological, but are the province of philosophers, theologians, politicians, and sociologists.

Ultimate Size Limitation If the world continues to grow at current rate, population will surpass 12 billion by 2060. Human population subject to same biological constraints as other species. Human population will ultimately reach a carrying capacity and stabilize. Disagreement about exact size and primary limiting factors.

Elephant Trade

Snow Goose (Pg.145)