Ch 40: Population Ecology and the Distribution of Organisms Flashcards
Define ecology
The scientific study of the interactions of organisms with each other and their physical environment
List and define the levels of the ecological hierarchy
- Organism → Population → Community → Ecosystem → Biosphere
- Organism -
- Population - All the members of the same species that inhabit a particular area
- Community - All the populations found in a particular area
- Ecosystem - A community and its physical environment, including both nonliving (abiotic) and living (biotic) components
- Biosphere - All of the ecosystems on Earth, including their biotic components
List the three factors that define a population
- Density: size/range
- Size: # of individuals of all ages alive at a particular time in a particular place
- Range: how widely a population is spread
- Demographics: The study of changes over time in the vital
- Growth Rate: change in number of individuals in the population over some unit of time
Briefly describe how population size is estimated
In some cases, population size and density can be determined by counting all individuals within the boundaries of the population. In most cases, however, it is impractical or impossible to count all individuals in a population. Instead, ecologists use various sampling techniques to estimate densities and total population sizes.
- They might count the number of oak trees in several randomly located 100×100 m plots, calculate the average density in the plots, and then extend the estimate to the population size in the entire area.
- In other cases, instead of counting single organisms, ecologists estimate density from an indicator of population size, such as the number of nests, burrows, tracks, or fecal droppings.
Distinguish between exponential and logistic growth
- Exponential Growth: Growth of a population in an ideal, unlimited environment. A population that experiences such ideal conditions increases in size by a constant proportion at each instant in time. This can occur in populations that are introduced into a new environment or whose numbers were drastically reduced by a catastrophic event and are rebounding.
- Logistic growth: Population growth that levels off as population size approaches carrying capacity
Define carrying capacity and explain why populations do not grow exponentially forever
- Carrying capacity - the maximum population size that a particular environment can sustain. Carrying capacity varies over space and time with the abundance of limiting resources. Energy, shelter, refuge from predators, nutrient availability, water, and suitable nesting sites can all be limiting factors.
- Crowding and resource limitation can have a profound effect on population growth rate. If individuals cannot obtain sufficient resources to reproduce, then the per capita birth rate will decline.
What does density-dependent environmental resistance factors mean?
This means that the effects on biotic potential are dependent on the size of the population
- Limited food supply
- Accumulation of waste products
- Increased competition
- Increased predation
- Disease
What does density-independent environmental resistance factors mean?
This means that the effects on biotic size potential are the same for all sizes of populations and are not dependent on size.
- Weather
- Natural disasters
Explain why hare and lynx populations oscillate
Predator and prey populations tend to cycle instead of maintaining a steady state
Define what a survivorship curve is
Survivorship curve - A plot of the number of members of a cohort that are still alive at each age; one way to represent age-specific mortality
- A cohort is a group of individuals born at the same time.
Identify and distinguish between Type I, Type II, and Type III survivorship curves
- A Type I curve is flat at the start and then drops steeply as death rates increase among older age-groups.
- Type II curves are intermediate, with a constant death rate over the organism’s life span.
- Type III curve drops sharply at the start but flattens out as death rates decline for those few individuals that survive the early period of die-off.
Explain what a Type I survivorship curve indicates
A Type I curve reflects low death rates during early and middle life, and then shows death rates increase among older age-groups. Many large mammals, including humans and elephants, that produce few offspring but provide them with good care exhibit this kind of curve.
Explain what a Type II survivorship curve indicates
Type II curves are intermediate, with a constant death rate over the organism’s life span. This kind of survivorship occurs in some rodents (including Belding’s ground squirrel), many invertebrates, lizards, and annual plants.
Explain what a Type III survivorship curve indicates
Type III curve reflects very high death rates for the young, but shows that death rates decline for those few individuals that survive the early period of die-off. This type of curve is usually associated with organisms that produce very large numbers of offspring but provide little or no care, such as long-lived plants, many fishes, and most marine invertebrates. An oyster, for example, may release millions of eggs, but most larvae hatched from fertilized eggs die from predation or other causes. Those few offspring that survive long enough to attach to a suitable substrate and begin growing a hard shell tend to survive for a relatively long time.
What does the term environmental resistance mean?
all those environmental conditions that prevent populations from reaching their biotic potential. These conditions can be density-dependent or density-independent.
