Understanding Populations

Chapter 8 page 210

What is a population?

• Population– All the members of a species living in the same

place at the same time.– Ex: bass in an Ohio lake– Reproductive group– Refers to the group and the size

Properties of Populations

• Described by– 1.Size, 2. density, or 3. dispersion

• Density– Is the number of individuals per unit area or volume.

• Ex: number of bass per cubic meter of water in a lake

• Dispersion– Is the distribution of its individuals within a given

amount of space.– Even, clumped, random

How does a population grow?

• 1.Gains by births• 2.Loses by death• Growth rate– A change in the size of a population over a given

period of time.• Equation– Change in pop size = births – deaths

• Growth rates can be 0, +, or –• Do all young survive to reproduce?

How fast can a population grow?• A species biotic potential is the fastest rate that

its population can grow.1. Reproductive potential– The maximum number of offspring that each member

of the population can produce– EX: elephant 750 yrs to produce 19 million

descendants vs. Bacteria produce that many in a few weeks

– 1.Produce more at a time,2. reproduce more often, and 3. reproduce earlier in life.

– Reproducing early shortens generation time.

How fast - Continued….

2. Exponential growth– populations grow faster and faster

• Occurs in nature if plenty of food & space and no competition/predators

• EX dandelions and starlings• Growth rate = change in population/time

What limits population growth?

1. Carrying capacity– – Is the maximum population that the ecosystem

can support indefinitely. – May increase above this but not for long. – Estimated by looking at average population sizes

or observing a population crash. – EX: rabbit population in Australia 1859

What limits growth- continued……

2. Limiting resource – species reach carrying capacity when it consumes a resource at the same rate the ecosystem produces it. That resource is a limiting resources.

Ex: what limits plants?

What limits growth- continued……

3. Competition– The member of a population use the same

resources in the same way. As the population reaches carrying capacity the will compete with each other.

– EX: mealworm larvae in a sack of flour. – Social Dominance or Territory– Territory includes space, shelter, food, breeding sites– Competition is part of natural selection.

2 types of population regulation

• Causes of death in population may be either:1. Density dependent – – Deaths occur more quickly in a crowed population.

Limited resources, predation, disease• EX: pine trees growing close together get infected by disease

carrying beetle.

2. Density independent– A certain proportion of the population dies regardless of

the population's density. Sever weather, natural disasters• EX: winter storm froze crops and fruiting trees