Exam 2 pt. 2 Flashcards
LV prey-predator isoclines and model dynamics
where there is no change in prey population = reaching a stable outcome (dN/dt = 0)
Competition and LV
crowding modifies the prey and predator zero isoclines because mutual interference among predators increases with their density and increased prey density and predators reach an upper density level
Mutual interference
the prey population can be limited by crowding through intraspecific competition (logistic limitation). Creates isoclines that are no longer neutrally stable, but are damped to converge to a stable equilibrium
Spatial heterogeneity
Aggregated prey show spatial heterogeneity (clumped distributions), and the prey isocline looks like Fig. 10.11, generating stable equilibria quickly (coexistence)
Pseudo-interference
generates an aggregation of risk among hosts of parasites; at high parasitoid density, attacked density, attacked hosts are more likely to have been parasitized already
Parasite
An organism that obtains its nutrients from one or a very few host individuals, normally causing harm but not causing death immediately
Microparasite
More common; Small, very numerous
Multiply directly in host
Mostly INTRAcellular - counted by number of infected hosts
Result in either death or some measure of host immunity
Macroparasite
Grow but Do not multiply in host
Produce infective stages to attack new hosts
Live INTERcellularly between tissues or on hosts
Can be counted individually
Multiply outside their host & host response varies according to parasite load
Parasite diversity
especially endoparasites, tend to live in very stable host environments
Large advantage against host immunity systems (especially endotherms)
Dispersal achieved through very high reproductive output
Develop defenses against the host immune responses
Diversity and abundance are also influenced by interspecific competition among parasites
Host diversity
Experimental host diversity mixtures can influence the spread of diease; can also limit the spread of disease infections;
Effectively diluted the density (contact rate) of susceptibles in the populations and reduces the effectiveness of vectors
Host survivorship
Reduced with increasing parasite load
Also reduction in age of maturity, fecundity and population rate of increase
Dynamics of parasite populations in hosts
Some degree of bottom-up control, in immune memory
Distributions of parasites within host populations also tend to be aggregated with only a few hosts carrying many parasites
Prevalence and intensity are related through various frequency distributions (shift according to nature of many diseases)
Prevalence of infection
the proportion of a host population that is infected
Intensity of infection
the number of parasites in or on a single host
Decomposers
Saprobes like bacteria and fungi that feed on dead or dying plant and animal tissue
Detritivores
feed on the same material once it has been fragmented and processed to varying extents by decomposers and physical events
Resources of decomposers
dead bodies of animals/carrion; feces and other excreted products; dead plant material
Primary distinction of decomposers/detritivores
Do not affect the rate at which their resources are produced; but predators/herbivores do
Host diversity
Effectively dilutes the density of susceptibles in the population and reduces the effectiveness of vectors
Host survivorship, age of maturity, fecundity, population rate of increase
reduced with increasing parasite load
Epidemic
Rp > 1
rapid increase in the incidence of disease with rapid infection of susceptibles
Endemic
Rp ~ 1
the rate of spread is much reduced by increased immunity, mortality and decreased density of susceptibles
Feeding guilds of herbivores
grazers, browsers, leaf miners, borers, root feeders, sap suckers, gallers, frugivores, seed predators, pollinators, nectarivores
Feeding guild
grouped on nature of exploitation (feeding the same way)
Effects of herbivory
Influence the distribution and abundance of plants through effects on plant parts, timing in plant development, post-attack effects (i.e., eating seedlings can change life history)
Herbivory Effects - Compensation
Herbivores almost always harm plants, although this may look like benefits
Increased Mortality (Herbivory)
repeated defoliation by herbivores can kill or make more susceptible to death
Reduced growth (Herbivory)
can slow or stop plant growth, but grasses tend to be resistant to the effects of grazing because the low meristem is unaffected
Plant fecundity reduction
smaller plants produce fewer or less viable seeds
Plants may flower later
Herbivores can eat reproductive parts directly
Herbivory
The interaction between PLANT DEFENSE and HERBIVORE FORAGING
“Optimal Defense” (plant defense theory)
Toxins (small)- effective against abundant generalist herbivores and may account for the effectiveness of some specialist herbivores Digestibility Reducers (large and expensive) - effective against both specialists and generalists by making nutrients less available to herbivores
Apparency
how easy it is to find in space/time
Continuous model of detritivory
dR/dt = F(R) - aP
R - resource renewal
F(R) - function of the amount of resource
P - number of predators
a - efficiency with which individuals find and capture their food resource
dR/dt - rate of resource renewal
Lotka-Volterra Predation Model
dN/dt = rN - aPN
Continuous model of detritivory - MUTUALISTS
dR/dt = F(R) + (delta) M
M - number of mutualists
(delta) - measure of mutual benefit dR/dt
Continuous model of detritivory - DECOMPOSERS AND DETRITIVORES
that have no influence on resource renewal
dR/dt = F(R)
Detritivores and microbivores
feed on bacteria and fungi
their food is often alive
taxonomically diverse
classified by size
Detritivores and microbivores by size
Microflora/fauna - <100 um (cold)
Mesoflora/fauna - 100 um - 2 mm (temperate)
Macroflora/fauna - 2 -20 mm (tropics)
Size groups are influenced by latitudes (biomes; niche distributions)
Diversity and abundance of detritivores - woodlands
in woodlands, microbial decomposition is highest
Large detritivores can enhance microbial respiration and function as a connected community (allantoin from woodlice??)
Diversity and abundance of detritivores - aquatic
separate into different guilds according to feeding methods (shredders, collector-gatherers, grazer-scrapers, collector filterers)
