topic 4 - density dependence in nature

Question 1

D-D best fit?

Answer 1

• Best fit for organisms growing by themselves (does not consider intraspecific competition, predation, parasitiism)
• Also best for organsims with fast life cycles and simple behavior
•

Question 2

what are some D-I factors

Answer 2

• Some (typically) D-I factors
○ (Impact on b and d doesn’t depend on density)
○ Weather events: drought, frost, flood, hurricanes
○ Human impacts :pollutants
Catastrophes: forest fires

Question 3

what are some D-D factors

Answer 3

• Some (typically) D-D factors 
		○ (impact on b and d depends on density) 
		○ Food 
		○ Space 
		○ Shelter 
		○ = competition for resources 
Natural enemies

Question 4

define competition

Answer 4

A reciprocally negative interaction between two or more individuals consuming, or attempting to consume, a single limiting resource

Question 5

define limiting resource

Answer 5

• Limiting resource:
Use by one individual reduces availability for use by another; and reduction in availability reduces b or increases d (changes equilibrium density or K)

Question 6

define the two types of competition

Answer 6

• Intraspecific competition:
○ Competition between individuals of the same species
• Interspecific competition:
Competition between individuals of different species

Question 7

plants compete for?

Answer 7

light
water 
mineral nutrients (N,P,K,fe)
space (above and below ground) 
depends on environment ie- temperate = light, deserts = below ground for water, agricultural= below ground for N

Question 8

animals compete for

Answer 8

• Food
• Space (e.g. nesting sites, shelter, territories, etc)
Mates

Question 9

describe exploitation competition

Answer 9

• Effect of one individual on another is indirect, via resource levels
• Consumption of resource by individual reduces supply to others
• Often no direct interaction
• Resources divided approx. equally; individuals suffer approx. equally from shortages
• more common, especially in plants
Can be intraspecific or interspecific

Question 10

inference competitions? what is alleopathy?

Answer 10

• Effect of one individual on another is direct, vs behavioral interaction
• One individual directly blocks another from access to resource (behavioral or chemical)
• Winners and losers (or losers and bigger losers - individual who wins loses time and energy)
• Common when resources are patchy (can be defended)
• e.g. water holes, salmon streams
Allelopathy: release of toxic chemicals in plants to suppress neighbors

Question 11

responses to competition?

Answer 11

1. Competition might affect b and d directly
   • Common for animals
   • Easily handled by D-D population growth models based on # of organisms/area (incorporates K)
   
   2. Competition may affect individual growth and development
      • Common in plants
      • E.g., a plant with lots of resources grows large & one with few
      resources stays small (but doesn’t necessarily die)
      • Biomass per unit area (as opposed to density of individuals)
      sometimes provides a better estimate of K for plants
      • Biomass also commonly used to monitor plant populations that
      are harvestable (forestry, agriculture)

Question 12

what two patterns connect plant competition and biomass

Answer 12

1. The law of constant final yield

The self-thinning rule

Question 13

describe the law of constant final yield

Answer 13

When density is high enough for intraspecific competition to be important, biomass yield Is constant regardless of plant density
• Extra individuals planted = balanced by reduction in individual
biomass (or mortality)
• Supports notion that biomass is better indicator of K for plants
•
Can change yield by changing resources

Question 14

self thinning rule

Answer 14

(trade-off) between population density & individual plant biomass when intraspecific competition is occurring (i.e., at carrying capacity)
• Linear relationship between log(individual biomass) log(density)
slope approx, -3/2
look at graph:
• Line represents biomass carrying capacity
• Plants grown at high densities can only gain biomass if density is reduced - self thinning

Question 15

thinning in forestry - why?

Answer 15

• Selective removal of trees, undertaken to improve the growth rate or health of the remaining trees.
Thinning grows bigger trees faster -more economic look at graph