Ecological Theory Exam Prep Flashcards
Study into changing variables in r-K synoptic population graph (SPG)
Southwood and Comins, 1976
What are the 6 main areas in the SPG and what do they mean?
1) Extinction valley - low population density, high risk of extinction at this point
2) Endemic range - initial growth rate increase stopping only when the first limiting factor comes into play, in most cases this being predators
3) Natural enemy ravine - The decrease in growth rate associated with enemy predation, usually an equilibrium is met with predators at this point
4) Release point - The point in which prey population density is higher than which natural enemies can reduce, thus resulting in an increase of population growth
5) Epidemic ridge - The escape from the natural enemy ravine which leads to rapid increase in population growth rate
6) Crash valley - Point in which natural resources are depleted and so the growth rate drastically declines
Key points about the extreme “r” end in the SPG
- Breeding occurs at very low densities and reproduction rate is very high, therefore the extinction valley is virtually absent
- Due to this high fecundity natural enemies are absent or insignificant, the population grows too quickly and thus there is no visible natural enemy ravine
- Population grows rapidly, being held at a high level before sharply falling
- This rapid growth in population allows the carrying capacity to be easily overshot
- Intraspecific competition, expressed as scramble competition (starvation, disease and migration) regulates population
Key points about the extreme “K” end in the SPG
- Long extinction valley as a result not only of low fecundity (as this is not always the case) but due to long reproductive life span
- Mortality due to natural enemies at this point is insignificant
- Equilibrium close to the carrying capacity is maintained at high density due to the long reproductive life span and the high survivability of the adult populations
What strategies do K-strategists employ that prevents them from going past the carrying capacity?
Low fecundity with high parental care - young protected from predators by adults (e.g. elephants)
High fecundity and high predation rate on young - only small numbers survive til adulthood through the following techniques;
- masting: synchronous production of massive nubers of young (e.g. periodic cicadas)
- Escape in time+space: adults produce young in different sites over long periods of time (e.g. rainforest butterflies)
Key points about the natural enemy ravine in the SPG
Middle section of the graph, between r and K
- natural predators have a major impact on the prey
- a number of variables though can impact these natural predators such as attack rate, handling time and predator abundance
- increase attack rate leads to a deepening of the ravine and widening almost entirely towards the low prey density
- increased attack rate may be the result of the predator density increasing in relation to prey, opposite also holds true
- significantly high populations of predators can reduce all populations below the release points to extinction
- Predator density increase leads to a decrease in growth rate of prey and a widening of the ravine
- the ravine starts shallow at the “r” end and at relatively low densities, begins to deepen before finally getting shallow again at the “K” end
What points does Southwood (1977) make on the control of “r” strategist pests?
- Many arable crop pests are within this category and so annual re-invasion is the key population pathway. It is then very effective to control if the difficulty of this pathway is maximised
- Changes to the overwintering or aestivating host sites are effective cultural techniques (Way, 1977)
- Manipulation of planting time to minismise synchronisation with pest species migration time very effective
- Utilising ecological bottlenecks, introducing biocontrol or insecticides during these points can be very effective
What points does Southwood (1977) make on the control of intermediate pests?
- When the intermediate pest is a native species, it is important that management strategies keep the natural enemy ravine in tact and widen if possible
What points does Southwood (1977) make on the control of “K” strategist pests?
- These are specialist pests and thus are sensitive to disturbance of habitat
- cultural techniques that change the habitat very effective (e.g. changing amount of shade)
- The low recruitment rate and complexity of K strategist reproduction make them highly susceptible to sterile male techniques
Study on locusts
Showler, 1995 case study
Desert locusts (Schistocera gregaria)
- Desert locust control organisation - Eastern Africa (DLCO-EA) operates over several countries collecting data, forecasting and providing early warnings of locusts in the member countries
- In 1993-94 widespread rain lead to widespread breeding of S.gregaria
- due to forecasting and appropriate action significantly reduced the damage caused by the plague in;
Sudan - August (420,000ha infested), September (40,000ha) October (nil)
Eritrea - July (9,000ha), August (3,600ha), September (nil)
- Using forecasting they tracked swarm and acted. Techniques used involved acting before 0900h (before swarm began movement), targeting nymphal bands (precluding adult stages) and allowed for the use of relatively selective, low residual insecticides (ULV)
Study on B.tabaci
Zaidi et al., 2017
- Host plant resistance
- Expression of insecticidal proteins and/or toxins or doublestranded RNA (dsRNA) homologous to B.tabaci genes was shown to provide plant with protection from B.tabaci and the begomoviruses they transmit
Study on NER
Barbosa, 1998
- Pecan pests, 3 aphid spp. infest pecans during season
- regulated by aphidophaga and ectomopathogenic fungi, but still produce honeydew damage to large extent
- cultural techniques to increase aphidophagous species survival implemented
- techniques include;
reducing pesticide spray frequency
planting legumes to act as intercrops in orchards to produce alternative prey aphids for aphidophaga
partitioning of foraging behaviour of imported red fire ants with trunk sprays of insecticides
Study into coconut rhinoceros beetle
Gressitt, 1953
- Coconut rhinoceros beetle (Oryctes rhinoceros) in Western Samoa
- complete eradication of the beetle from one of the islands
- done so by destroying breeding grounds (rotten logs) and use of coconut log traps
