Lecture 9 - PowerPoint PPT Presentation

Lecture 9

BIOL 3500

Chapter 11: Intraspecific Population Regulation

• Contrast:
• Density dependance vs. independence
• Scramble vs. contest competition
• Home range vs. territory
• Define:
• “Self thinning”
• Philopatry
• Discuss:
• Effects of crowding

• Refers to factors regulating population, effect is proportional to pop size.
• Number of indiv affected depends upon intensity.
• Ex: food limitation, communicable disease

• Density dependent factors can affect either or both

• Refers to pop-infuencing factors not influenced by pop size.
• Typically what we call “natural disasters”
• Ex: hurricanes, fire

• Will occur any time there are more individuals than a resource can support
• One resource will limit
• If it becomes plentiful, another resource will become limiting

• Intraspecific
• Between individuals of the same species (Chapter 11)
• Interspecific
• Between individuals of different species (Chapter 14)

• Scramble competition
• All individuals are depressed equally
• Too many pine trees planted in a forest (all will be small)
• Contest competition
• Some individuals are better at getting limited resources
• Baby birds in a nest (big one gets most of food)

• Tadpoles grown in higher density population have lower mean body mass
• Slower to reach maturity
• Presumably compete for food

• White clovers grown at high density have decreased mean weight

• When stocked at high density, only small fish result
• May never reach breeding size
• Careful monitoring of size, control of stocking rates important
• MSU website
• NC State website

• We already knew that limited resources cause reduced growth
• We saw that competition causes limitation in resources, and affects growth
• Is the response of an organism in competition different in intensity than just resource limitation?

Two types of pots: 1 plant vs. 16 plants

Broadleaf Peppermint

Note: water is per pot

Limitation + competition interact! (shape of curves is different)

• Unlike pine trees, tadpoles, or bluegills, horseweed is “self thinning”
• If too crowded, competition will kill some

Fecundity of females can change under competition

Most notable in large mammals

Bison have sharp drop

Grizzly bears affected linearly

• Age of sexual maturity depends upon population density

Corn and salt marsh plants

• List all the ways that intraspecific competition can regulate a population.

• Crowding may cause increased aggression
• Stress causes hormone changes, resulting in:
• Retarded growth rate
• Delayed onset of reproducton
• Reproductive failure (miscarriage, low birth weight)
• Immune system compromise

• Among wolves, usually only alpha male and alpha female mate
• All others are prevented from doing so
• When food becomes limiting, subordinates are chased out of the pack
• Lone wolves have harder time hunting (mortality increases)

• Home range = area used by one individual over a year
• Size often depends upon food needs
• Type of food
• Amount (ie: body size of individual)
• Sex matters too. Males’ ranges generally bigger. Why?

• Territory = part of the home range, actively defended
• Birds might sing, display, fight for an area
• Grasshopper sparrows return to same territory yearly (philopatry)