How populations grow and Limits to growth

Three important characteristics of a population are 1. Geographic distribution 2. Density 3. Growth rate Characteristics of Populations

A term that describes the area inhabited by a population. Vary in size. Geographic distribution (range)

Number of individuals per unit area. PD = number of individuals / unit area OR PD = number of individuals divided by unit area Population Density

Three factors affect population size: 1. Number of births 2. Number of deaths 3. Number of individuals that enter or leave the population. Immigration – movement of individuals into an area. Emigration – movement of individuals out of an area. Population Growth Rate

Animals emigrate. Decline Animals immigrate. Growth More births than deaths. Growth More deaths than births. Decline Same number of deaths to births. Stays the same Population growth or decline?

Two types of population growth graphs 1. Exponential growth 2. Logistic growth Population growth graphs

Exponential growth A population with  Abundant space  Abundant food  Protected from predators and disease Under ideal conditions with unlimited resources, a population will grow exponentially.

Logistic Growth As resources become less available, the growth of a population slows or stops. Occurs when a population’s growth slows or stops following a period of exponential growth.

Logistic Growth Carrying capacity – the largest number of individuals that a given environment can support Consider your own house’s carrying capacity.

Review Break! Suppose that the total penguin population was 1200 at the beginning of the year and 1600 at the end of the year. What was the population’s growth? Answer: increase of 400 penguins Suppose 250 penguin chicks died during the year. What was the population’s growth? Answer: Net increase of 150 penguins Suppose that 200 adult penguins also died during the year. What was the population’s growth? Answer: A net decrease of 50 penguins

Review Break! List three characteristics that are used to describe a population. Answer: Geographic distribution, density, growth rate What is the equation for population density? PD = number of individuals/unit area What is carrying capacity? Answer: largest number of individuals that a given environment can support.

What is a specific limiting factor we have discussed before? Limiting nutrient Limiting factor – a factor that causes population growth to decrease Examples: Competition, predation, parasitism/disease, drought and other climate extremes, human disturbances Limiting factors

A limiting factor that depends on population size Examples: Competition, predation, parasitism, and disease. Density-dependent limiting factor

When populations become crowded, organisms compete with one another for food, water, space, sunlight, and other essentials. Competition occurs between members of the same species and different species. Density-dependent limiting factor Competition

Regulation of a population by predation takes place within a predator-prey relationship – population control Density-dependent limiting factor Predation

First, why is this density-dependent? Parasites are like predators – take nourishment at expense of hosts, often weakening and causing disease or death. Density-dependent limiting factor Parasitism and Disease

Affect all populations in similar ways, regardless of the population size. Examples: Unusual weather, natural disasters, seasonal cycles, and certain human activities – such as damming rivers and clear-cutting forests Density-independent factors

Contrasting density-dependent/density- independent 1. Competition 2. Human activities 3. Predation 4. Parasitism 5. Unusual weather 6. Disease 7. Natural disasters Review Break!

Are density-dependent limiting factors abiotic or biotic factors? Answer: Biotic factors Are density-dependent limiting factors abiotic or biotic factors? Answer: Abiotic factors Review Break!