Ecological Theory Flashcards
What are the reasons for pest outbreaks?
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
What does the r in the r-K continuum signify?
r = growth rate
- no. born - no. die
- positive r always results in a sigmoid plotting on a graph
What is the calculation for growth rate?
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
What does the K signify int he r-K continuum?
K = carrying capacity
i.e. the amount of population an area can support
What factors affect K?
space, food, access to mates etc.
What happens as populations reach K?
Birth rates decline and death rates increase
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?
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
What is the final equation of the r-K continuum?
dN/dt = rN*(K-N)/K
dN/dt = rate of change of population size N with time t
What favours species that exist near K (high densitites) and what favours those that exist near r (low densities)?
K = favours stable resource use through competition r = favours rapid reproduction
What are the characteristics of an r-selected species?
- 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
What are the characteristics of a K-selected species?
- Usually exist in stable habitats (in high densities)
- long maturation
- long lifespan
- low mortality rates
- low fecundities
- parental care
- often large
What are the three main regions in the synoptic model of population growth?
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
What are the characteristics of r-selected pests?
- Unstable environments
- high fecundity
- small size
- very dispersive
- ideally suited to temperate crops
Damage is largely a function of numbers
What are the characteristics of K-selected pests?
- Stable environments
- low fecundity
- large size
- not dispersive
- specialised feeding
- competitive
Damage is largely a function of type rather than numbers
What are the characteristics of intermediate species pests?
Species affected in their dynamics by the actions of predators i.e. species affected by the natural enemy ravine
What are the main pest management techniques?
Cultural Biological Reproductive/Genetic Host-Plant Resistance Chemicals
Name some r-selected pests and there statistics
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)
How are r-selected pests managed?
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)
Why are K-selected pests a problem?
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
Give examples of K-selected species and their stats
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)
How are K-selected pests managed?
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)
How can intermediate pests be managed?
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
What do the terms R^2 and multiple R (r) mean in an ANOVA test?
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))
