Lecture 11: Resources and Competition

Question 1

Resource definition with regard to effect on pop growth

Answer 1

Anything an organisms consumes or uses that causes an increase in pop growth rate when it becomes more available

sunlight, water, soil nutrients, food space

Question 2

Liebig’s Law

Answer 2

A population increases until the supply of the most limiting resource prevents it from increasing further

Question 3

Tilman’s R (resource conversion efficiency)

Answer 3

dN/dt = ceRN - mN

c = consumption rate
e = efficiency of conversion
r = resource abundance
m = natural mortality

Question 4

Tilman’s R - formatted for R

Answer 4

R = m/ce

If R1 < R2, species 1 will win competition

Question 5

Tilman’s R example (hornsnails v. Japanese false cerith)

Answer 5

• Cerith wins from lower resource conversion efficiency
• trematode parasites in mud snails –> apparent competition
• native snails more likely to suffer negative effects from infection

Question 6

Tilman’s Resource Model of Succession

Answer 6

Changing resource conditions means one species may be replaced by another

Question 7

Fundamental niche

Answer 7

all the combinations of conditions a species could occupy

Question 8

Realized niche

Answer 8

subset of combinations in which a species actually persists

Question 9

What does Darwin argue regarding competition and natural selection?

Answer 9

Competition is most intense between closely related species due to similar traits and consumption of similar resources
* natural selection should favor differences in habitat use

Question 10

Tansley 1917 - Common Garden

Answer 10

• Heath bedstraw grows mostly on acidic; white grows mostly on alkaline
• plant two species separately and together in boxes of acidic or alkaline soils
• each species grew best in soil type of natural habitat
• each outcompeted other in own natural soil type

Question 11

Blue mussels example for niches

Answer 11

• restricted by predation –> increases diversity
• lower distribution of mussels in absence of sea stars extends to low/mid intertidal –> mussels become dominant competitor for space
• Sea star as “keystone” predator –> gradients in abiotic conditions and biotic forces create zonations

Question 12

Character displacement as an evolutionary solution to competition

Answer 12

• strong competition favors resource partitioning/niche differentiation –> reduce “niche overlap”
• ex. MacArthur’s warblers - niche differentiation on feeding and nesting times/space on trees