Limits to Population Growth
Stress from overcrowding
- Species can fight amongst themselves if overcrowded - Fighting can cause high levels of stress, which can weaken the bodies ability to resit disease - lower immune system - Can cause lower birthrates, raise death rates, or both. Can also increase emigration.
Describe the general trend of human population growth over time
most of human existence: slowly increased last 500 years, the human population has been growing more rapidly.
List 3 density-dependent limiting factors
predation, herbivory, parasitism, disease, stress from overcrowding
Exponential human population growth
as civilization advanced, life became easier, and the human population began to grow more rapidly - espesically during the Industrial Revolution when food became more reliable - nutrition, sanitation, medicine and healthcare dramatically reduced death rates
What is a density-independent limiting factor?
A factor that affects populations regardless of their size or density ( unusual weather, natural disasters)
What is a limiting Factor?
A factor that controls the growth of a population
Limiting Factor
A factor that controls the growth of a population. Limiting factors keep most natural populations somewhere between extinction and overrunning the planet. - Some limiting factors include competition, predation, parasitism, and disease, which depend on population density - Others are natural disasters which do not depend on population density
Why do population growth rates differ among countries?
Birthrates, death rates, and the age structure of a population help predict why some countries have a high growth rates while other countries grow more slowly
What limiting factors depend on population density?
Density-dependent limiting factors include competition, predation, herbivory, parasitism, disease, and stress from overcrowding
Why do populations in different countries grow at different rates?
Different countries have different sizes and densities, and resources.
Density-independent limiting factors
affect all populations in similar ways regardless of population size and density
Demographic Transition
High birthrates and death rates, to low birthrates and death rates ( Us, Japan, and Europe have completed it)
Parasitism and Disease
Parasitism and Disease are density dependent because the denser the host population, the more easily parasites an spread from one host to another
Malthus Theory
Population will grow exponentially until something checks population growth (war, famine, disease, etc)
predation and herbivory
Predator Prey relationships may cycle. For example: When wolves have plenty to eat their population grows, and they kill more moose than are born. This causes the moose death rate to rise higher than its birthrate, so the moose population falls. As the moose population drops, wolves begin to starve. Starvation raises the wolves' death rate and lowers their birthrate, so the wolf population also falls. Herbivore Effects are similar to those of predation Humans as predators: Sometimes, humans actively limit the population - We catch more and more cod every year, so the cod population is decreasing.
How has human population size changed over time?
The human population, like populations of other organisms, tends to increase. The rate of that increase has changed dramatically over time. - human population grew slowly because life was harsh (little food, diseases were common)
What limiting factors do not typically depend on population density?
Unusual weather ( hurricanes, droughts, floods) and natural disasters (wildfires)
Competition
When populations become crowded, individuals compete for food, water, space, sunlight, and other essentials. Some obtain enough to survive and reproduce, while others survive and can't reproduce, while others starve to death or die from lack of shelter. - Competition can lower or increaser birth/death rates - Competition is density dependent because the more individuals live in an area, the sooner they use up the available resources
