Ecological Theory

Question 1

What are the reasons for pest outbreaks?

Answer 1

Attempts to improve food production
- monocultures
- high yielding varieties
- continuos cropping
Reductions in predators
- could be caused by chemical use or habitat destruction
Global trade and pest species movement
Consumer tastes

Question 2

What does the r in the r-K continuum signify?

Answer 2

r = growth rate

• no. born - no. die
• positive r always results in a sigmoid plotting on a graph

Question 3

What is the calculation for growth rate?

Answer 3

N(t)=N(0)*e^rt
N(t) = population after time "t"
N(0) = initial population (when t = zero)
e = constant (2.718)
r = relative growth rate
t = time

Question 4

What does the K signify int he r-K continuum?

Answer 4

K = carrying capacity

i.e. the amount of population an area can support

Question 5

What factors affect K?

Answer 5

space, food, access to mates etc.

Question 6

What happens as populations reach K?

Answer 6

Birth rates decline and death rates increase

Question 7

What calculation shows the number of individuals still able to be added to a population before carrying capacity is met and what calculation shows this as a fraction?

Answer 7

K-N = number of individuals that can be added
(K-N)/K = fraction of K still available

e.g. K=100 & N=50
(100-50) = 50 more can be added
(K-N)/K
(100-50)/100
= 1/2 K still to go

Question 8

What is the final equation of the r-K continuum?

Answer 8

dN/dt = rN*(K-N)/K

dN/dt = rate of change of population size N with time t

Question 9

What favours species that exist near K (high densitites) and what favours those that exist near r (low densities)?

Answer 9

K = favours stable resource use through competition
r = favours rapid reproduction

Question 10

What are the characteristics of an r-selected species?

Answer 10

• Tend to use unstable habitats existing most of the time at low densities (rarely reaching K)
• rapid maturation
• short lifespan
• high mortality rates
• high fecundities
• no parental care
• often small

Question 11

What are the characteristics of a K-selected species?

Answer 11

• Usually exist in stable habitats (in high densities)
• long maturation
• long lifespan
• low mortality rates
• low fecundities
• parental care
• often large

Question 12

What are the three main regions in the synoptic model of population growth?

Answer 12

r-end: rapid population growth and rapid population crash
K-end: low population growth, species at equilibrium
Natural enemy ravine: Characterised by 2 values of K

Question 13

What are the characteristics of r-selected pests?

Answer 13

• Unstable environments
• high fecundity
• small size
• very dispersive
• ideally suited to temperate crops
  Damage is largely a function of numbers

Question 14

What are the characteristics of K-selected pests?

Answer 14

• Stable environments
• low fecundity
• large size
• not dispersive
• specialised feeding
• competitive
  Damage is largely a function of type rather than numbers

Question 15

What are the characteristics of intermediate species pests?

Answer 15

Species affected in their dynamics by the actions of predators i.e. species affected by the natural enemy ravine

Question 16

What are the main pest management techniques?

Answer 16

Cultural
Biological
Reproductive/Genetic
Host-Plant Resistance
Chemicals

Question 17

Name some r-selected pests and there statistics

Answer 17

Locust - fecundity (400), generation time (1-2 months), Damage (any crop)
Bean Aphid (Fec. 100), (Gen. 1-2 weeks), (dam. many crops)
Housefly - (Fec. 500), (Gen. 2-3 weeks), (dam. waste)
Cutworms - (Fec. 1500), (Gen. 1-2 months), (Dam. seedling)

Question 18

How are r-selected pests managed?

Answer 18

Populations for r-selected pest species fluctuate widely so look for ecological bottlenecks (when populations are low in number)

• Use of chemicals when population is at it’s lowest, manipulate planting dates to avoid periods of dispersal
• Monitoring and forecasting may help enormously (cultural)

Question 19

Why are K-selected pests a problem?

Answer 19

Damage is largely a function of type e.g. often cosmetic in agricultural situations (codling moth)
Damage may be because of new associations e.g. tsetse fly
Damage may occur because natural regulation is altered e.g. elephants

Question 20

Give examples of K-selected species and their stats

Answer 20

R.Beetle - (Fec. 50), (Gen. 3-4months), (Dam. coconut)
Tsetse - (Fec. 10), (Gen. 2-3months), (Dam. vector)
Codling Moth - (Fec. 40), (Gen. 2-6months), (Dam. fruit)

Question 21

How are K-selected pests managed?

Answer 21

Well adapted to habitats and thus habitat disruption may help
Genetic methods such as Sterile Insect Release Techniques (SIRT) may help - improves as population declines (only method to do so)

Question 22

How can intermediate pests be managed?

Answer 22

Species that are largely held below their maximum K by the action of natural enemies - range across whole r-K continuum
- become pests when natural enemy ravine does not exist
Boosting or replacing natural enemy ravine may help manage these pests
- intorduciton of biocontrol agents
- habitat manipulation to improve natural enemy numbers
- selective chemicals
- spot sprays. strip sprays, reduced rate applications

Question 23

What do the terms R^2 and multiple R (r) mean in an ANOVA test?

Answer 23

R^2 = coefficient of determination (how close data fits to the regression line)
Multiple R = correlation coefficient (always between -1 and 1, measures how correlated the two results are (x and y))