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Lecture 9

Lecture 9 BIOL 3500 Chapter 11: Intraspecific Population Regulation Learning Objectives Contrast: Density dependance vs. independence Scramble vs. contest competition Home range vs. territory Define: “Self thinning” Philopatry Discuss: Effects of crowding Density Dependence

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Lecture 9

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  1. Lecture 9 BIOL 3500 Chapter 11: Intraspecific Population Regulation

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

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

  4. Birthrate & Mortality Rate • Density dependent factors can affect either or both

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

  6. Competition • 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

  7. Two Types of Competition • Intraspecific • Between individuals of the same species (Chapter 11) • Interspecific • Between individuals of different species (Chapter 14)

  8. Two More Types of Competition • 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)

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

  10. Crowding and Clover • White clovers grown at high density have decreased mean weight

  11. Bluegills and Crowding • 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

  12. Question • 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?

  13. Competition and 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)

  14. 7th Inning Stretch

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

  16. Reproduction & Interspecific Competition Fecundity of females can change under competition Most notable in large mammals Bison have sharp drop Grizzly bears affected linearly

  17. Harp Seals • Age of sexual maturity depends upon population density

  18. Fecundity and Plants Corn and salt marsh plants

  19. Quick Review: • List all the ways that intraspecific competition can regulate a population.

  20. Stress and Competition in Animals • 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

  21. Social Dominance • 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)

  22. Home Range • 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?

  23. Diet, Body Size, and Home Range

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

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