Chapter 5 Populations 5 1 How Populations Grow

Chapter 5: Populations

5. 1 How Populations Grow? Describing Populations How do ecologists study populations? n Populations are studied by ¡ ¡ Geographic range Density and distribution Growth rate Rate structure

Geographic Range n n Area inhabited by a population Can vary in size depending on the species

Density & Distribution n The number of individuals of a particular species at a specific place. The number of individuals per unit area. Distribution refers to how individuals in a population are spaced out across the range of the population. ¡ Random, Uniform, Clumped Refer to Fig 5 -2 For Example: the number of alligators per square mile of the everglades population = individuals = 400 alligators = 10 alligators density unit area 40 km 2 By measuring the population density of a specific species can give us a better idea of the effects of the environment in a specific area.

Patterns of Distribution

Growth Rate n Indicates whether the size of a population increases, decreases or is sustained.

Age Structure n The number of males and females of each age contained in a population.

Population Growth What factors affect population growth? q The factors that can affect population size. n n n q birthrate death rate immigration & emigration rates It depends on how many individuals are added or removed.

Exponential Growth q Is the growth of a population by a constant factor at constant time intervals. q Unlimited resources and absence of predation and disease, population will grow exponentially.

Logistic Growth n When a population’s growth slows and then stops following a period of exponential growth.

Phases of Growth n n n Phase 1: Exponential Growth Phase 2: Growth Slows Down Phase 3: Growth Stops

The Logistic Growth Curve n It occurs when a population’s growth slows and then stops, following a period of exponential growth.

Carrying Capacity ¡ ¡ ¡ Maximum number of organisms in a population that an environment can maintain. When birthrate and the death rate are the same. When immigration equals emigration.

Carrying Capacity n The population of seals before the early 1900’s kept this population below its carrying capacity. After the hunting was reduced, the seal population increased exponentially until it reached its carrying capacity. This Sshaped curve indicates a rapid increase in population for a period of time that will stabilize after reaching carrying capacity of the environment. Carrying Capacity Video

5. 2 Limits to Growth What factors determine carrying capacity? q Condition that restricts a population's growth, such as space, disease, and food availability.

Density-Dependent Limiting Factors ¡ Factor that limits a population more as population density increases. n Competition n Predation n Herbivory n Parasitism n Disease n Stress from overcrowding

Competition When populations become crowded, individuals compete for: n Food n Water n Space n Sunlight n Territories n Other essentials

Predation and Herbivory • Predator. Prey Relationships • Herbivore Effects • Humans as Predators Refer to pages 138 -139

Parasitism and Disease Parasites and disease causing organisms feed at the expense of their host, weakening them and often causing disease or death.

Stress From Overcrowding High level of stress can weaken the body’s ability to resist disease or it can cause females to neglect, kill, or even eat their own offspring. Limiting Factor video

Density-Independent Factors What limiting factors do not typically depend on population density? Unusual weather such as hurricanes, droughts, floods. Natural disasters such as wildfires. Fig. 5 -10 Limiting Factors Video

5. 3 Human Population Growth How has human population size changed over time? The human population, like populations of other organisms, tend to increase.

Historical Overview n n n The human population has increased explosively. Wide-scale farming began to replace hunting and gathering, providing a more plentiful food supply. More food meant people reproduced more and lived longer, and the population began to climb. In the past few centuries, death rates have continued to decline because of improvements in nutrition, sanitation, and health care.

Predicting Future Population Growth n n A city population's demands for food, water, energy and other supplies can strain resources far from the city. New technology, especially in agriculture and medicine, enabled more people to survive and reproduce.

Patterns of Human Population Growth Read Page 144 Refer to Fig 5 -12 Over Population video