Download (De)stabilizing Factors

(De)stabilizing Factors
• Models assume no competition among predators, type I
functional response.
• Predator/prey population may be stabilized or
destabilized by:
– Mutual interference (reduce predator effectiveness)
– Different predator functional response (reduce
predator impact on prey)
– Density dependence or other specific predator/prey
population dynamics
• Ratio dependent predation
– Predation rate (and therefore predator population rate
of increase) is a function of the predator:prey ratio.
(De)stabilizing Factors
• Allee Effect – recruitment disproportionately low at low
density, producing a hump shaped prey isocline
– High efficiency type II predator destabilizes
– Lower efficicncy type II predator stabalizes
• A predator isocline to the left of the hump destabilizes
oscillations.
(De)stabilizing Factors
• (a) and (b) Similar to
Lotka-Volterra,
isoclines curved to
reflect density
dependent effects.
• (c) ratio dependent
predation
• (i) – moderate
predator efficiency,
least stable
• (ii) – less efficient,
more stable
• (iii) – Predator self
limitation, no
oscillations, low P.
(De)stabilizing Factors
• A type III predator switching
among several potential prey
– (i) More efficient predator is
stabilizing while less
efficient predator (ii) is less
stabilizing
• may have a stable population
independent of individual prey
populations.
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Multiple Equilibrium Points
Patch Dynamics and Predator-Prey Interactions
• Adding patchiness
increases complexity,
we know patchiness is
inherent in all
biological systems.
• What does patchiness
do to predator-prey
systems?
(a) habitat
(b) habitat
Detritivores and Decomposers
• Typical consumer – consumer takes from resource from
prey, prey fitness negatively effected (+/-)
• Donor controlled system – waste products donated to
consumer (detritivore or decomposer).
• Decomposition has no adverse effect on donor (+/0) and
there may often be an indirect mutualistic effect (+/+).
Tertiary Consumer
• Allee effect combined with type III functional response
produces prey isocline with hump and vertical section at
low N
• X, Y and Z are all stable equilibrium points, possible
explanation for outbreaks of particular species.
Detritivores and Decomposers
• Nutrient Source
– Parts of modular organisms
– Parts of unitary organisms
– Carcasses
– Feces
• Carnivore feces less desirable than herbivores
• Nutrient fate
– Immobilization
Secondary Consumer
– Mineralization
Primary Consumer
Primary Production
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Detritivores and Decomposers
•
•
•
•
Cellulose and Chitin
Mostly bacteria and fungi
Food for decomposers is extremely
patchy (feces, carcass etc.)
Good colonization, succession and
competition model
– Understudied, historical
taxonomic difficulties
•
Energy tied up in cellulose or
chitin not usually
physiologically digestible.
•
Cellulase and chitinase
enzymes restricted almost
entirely to microbial
decomposers.
Good dispersers/colonizers utilize
easy nutrients first, later colonizers
outcompete for more difficult
nutrients
•
Two sided debate
– Organisms use cellulose
and chitin to be less
digestible (poorer prey
quality, OFT)
– No selection to produce
chitinase or cellulase when
you can rely on microbial
symbionts.
Symbiosis and decomposition
• Considerable energy not physiologically digestible by
animals
– Internal and/or external rumen – compensation for lack of
cellulase?
– Coprophagy
Microbivores
• Microbivores – protozoan consumers of bacteria and
yeasts.
• Decomposing material supports a diverse community.
• Different taxa play different roles in decomposition.
Greater diversity=greater rate of decomposition though
facilitation.
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Decomposition in major types of ecosystems
• Streams, small lakes,
terrestrial – input is large,
heavy in cellulose,
shredder types necessary.
– River Continuum
Concept
Coprophagy and Autocoprophagy
•
•
Feed on others feces – plant
material is mechanically
digested, has microbial
community
Feed on your own feces –
pass material through your
own digestive system, process
twice
Large bodied detritivores
•
Most nutrients come from
meiofauna, microbivore fauna
•
Probably best described as
omnivores, diet composed
mostly of decomposers, not
actual “detritus”.
•
Detritivore dominated
communities – low/no
productivity compared to outside
organic contribution.
•
Allochthonous vs autochthynous
organic input
Carion Specialists
• Large non-plant
carcasses are a high
quality meal
• Sucession similar as
in plant detritus,
except that energy is
more readily
available (no
cellulose), but tends
to be patchier.
• Eg. American
burying beetle,
hagfish, maggots
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