module 12 Flashcards
exploration can affect competition consumer-resource(exploitation) detritivore-detritus mutualism
a population (-)(-) (+)(-) (+)(0) (+)(+)
Exploitation predators parasistes parasitoids pathogens
Interaction between populations
Enhances fitness of one individual while reducing fitness of the exploited individual.
Predators – Kill and consume other organisms.
Parasites – live on host tissue and reduce host fitness
Do not generally kill the host.
Parasitoid – insect larva that consumes the host.
Pathogens induce disease.
3 Feeding Methods of Heterotrophs:
Herbivores: Feed on plants.
Carnivores: Feed on animal flesh.
Detritivores: Feed on non-living organic matter.
Herbivory grazing browsing granivore frugivory nectivory
Consumption of plants or plant parts Grazing – eating grass or forbs Browsing – Eating leave or young shoots Granivory – seed predation Frugivory – consumption of fruiting bodies Nectivory – consumption of nectar
Substantial nutritional chemistry problems
Plant composition differs from Animal composition
-plants have ____ concentrations
must overcome plant defenses
physical and chemical
low nitrogen concentrations
Must overcome plant defenses Physical Thorns Waxes & Resins Cellulose, lignin, silica
Chemical
Toxins
Digestion Reducing Compounds
Detritivores consume food rich in often poor in dead leaves has fresh detritus may still have
Consume food rich in carbon and energy
Often poor in nitrogen
Dead leaves may have half nitrogen content of living leaves.
Fresh detritus may still have considerable chemical defenses present.
Carnivores
consume ______ preg
can’t choose prey at will
Consume nutritionally-rich prey Cannot choose prey at will -Availability & Capturability of prey -Risk involved -Select whole organisms Not nutrients
-Most are well balanced nutrtionally
May selectively consume parts
predators and seed predators
high probability of death low duration of association
parasitoids
high death high association
grazers and browsers
low death short duration
parasites and anrthropod herbivores
low death high high durations
Parasites That Alter Host Behavior
Spring-Headed Worm (Acanthocephalans)
- Changes behavior of amphipods
- Make it more likely that infected amphipods will be eaten by a suitable vertebrate host.
- Infected amphipods
- Swim toward light
- Usually indicative of shallow water
- Closer to predators.
-make it susceptible to predators to continue life cycle and spread
Herbivores Effect on Plants
short term effects
Short Term Effects -strict negative-decreases when fed on compensation Morphological & physiological adjustments counter losses up to a threshold -compensate for loss -after a while can't compensate
Overcompensation
increase in performance, growth, or fitness under low to moderate grazing
Long Term Effects?
why does Compensation occur
increased Plant Activity
Timing & Intensity
Increased Ecosystem Functioning
-nutrients go back to increase production through feces or death
Elton
and Keith
proposed driven by variation in solar radiation.
increase radiation, increase production-population goes up at the same time cycle
Keith- Suggested overpopulation theories: Decimation by disease and parasitism. Physiological stress at high density. Starvation due to reduced food. -overpopulation occurs decrease because of stress disease starvation
Snowshoe Hares - Role of Food Supply
In winter browse on buds and stems Shrubs and saplings such as aspen and spruce 2 Effects Greatly reduce Food Supply Greatly reduce food biomass Late November = 530 kg/ha Late March = 160 kg/ha ~ 70% reduction in food supply Alter Food Supply Shoots produced after heavy browsing Increase levels of plant chemical defenses Reducing usable food supplies
-increase chemical defenses when hares feed heavily, this makes it harder to get nutrients and causes decrease of hares- easy to prey Ono
Snowshoe Hares - Role of Predators
Predation
60-98% of mortality during peak densities.-easier prey since they have no more nutrients they ate it all
Lynx
Classic specialist predator
Other Specialist predators have similar responses
Coyotes may also play a large role.
Complementary role of predations & Food:
Hare populations increase
Causes:
Food supplies to decrease
Starvation and weight loss
May lead to increased predation
All decrease hare populations
Lotka-Volterra assumes Host population :
limited by
Grows exponentially
limited by parasites, pathogens, and predators:
rhNh =
Exponential growth by host population.
Opposed by:
p =
Nh =
Np =
p = rate of parasitism / predation. Nh = Number of hosts. Np = Number of parasites / predators.
Lotka Volterra assumes:
Parasite/predator growth rate is determined by:
- Rate of conversion of food into offspring
- Minus mortality rate of parasitoid population:
c p Nh Np
Conversion rate of hosts into offspring.
p Nh Np
Rate at which exploiters destroy hosts.
c=
Conversion factor
-Rate at which prey biomass transformed into predator offspring
Model Behavior
Host(prey) population dynamics
more predators=
larger predator population eventually
in turn ______ predator population
Growth
-Exponential
- Growth opposed by exploitation.
- -Host reproduction immediately translated into destruction by predator.
- –Increased predation = more predators.
- –More predators = higher exploitation rate.
- –Larger predator population eventually reduces host population
- –In turn reducing predator population.
increase in predation=_______ in exploration
decrease prey=_____ predators consumption
increase in exploitation
decrease predators consumption
Reciprocal effects produce oscillations in two populations.
Assumptions of Lotka-Volterra Result in:
Eternal oscillations
Neither host nor exploiter populations are subject to carrying capacities
-prey and predator balance each other out
Assumptions of Lotka-Volterra
Unrealistic
- Lack of Carrying Capacity
- No consideration of Outside Factors
-Valuable contributions to the field
Animals Respond to Changing Food Densities in one of 2 ways
Functional Response
Numerical Response
Numerical Response
as prey pop. increases
A change in the population size of a predator species as a result in the density of its prey
-Migration
-Population Growth
predator pop. increases
Functional Response
A change in the rate of exploitation of prey by an individual predator as a result in a change in prey density
Holling described (3) basic functional responses: Type I.
- Feeding rate increases linearly as food density increases - levels off at maximum.
- Consumers require little or no search and handling time.
- filter feeders whale
- constant linear
Type II.
Feeding rate rises in proportion to food density
Feeding rate partially limited by search/handling time
Type III.
Feeding rate increases most rapidly at intermediate densities
(S-shaped).
Type II Functional response
Trade-offs of Time Constraints
Th and TS
Handling Time (Th) Search Time (Ts)
Hollings Disc Equation
E
H
A
E = (aHT) / (1 + aHTh)
E – Number of Encounters
H – Prey Density
a – Searching Efficiency
handling time longer =
handling time smaller=
less encounter
more encounter, more prey attack
Type III Functional Response
Low prey density
Low prey density
-Predators respond slowly
Intermediate prey densities
-Consumption rate highest
Allows Regulation of Prey populations
-Pressure Relieved at low Densities
Factors for Type III
-prey vulnerability
search time and motivation
search an capture vulnerability
Prey Vulnerability
- Heterogeneous Habitat
- > Limited Hiding Cover
Search Time & Motivation to Hunt prey item
-Search Image
Search & Capture Vulnerability
- Lack of Reinforcement of Search Behavior
- Prey Switching
Search Images
high densities _____search images
- A behavioral prey selection mechanism
- -Enables predators to increase searching efficiency for prey that are abundant and worth capturing
- High Densities reinforce Search Images
-select prey that are more abundant and worth capturing
Prey switching
- Predators often choose most abundant prey in greater proportion than it is found
- Energetic Constraints
Optimal Foraging Theory
- Predators Choose Food items
- Confronted with numerous Choices
- -Potential Cost
- -Exposure to risks (predation, injury, etc.)
- -Energy Expenditure
- Potential Benefits
- Choice Minimizes Cost relative to Benefits
- Predicts that natural selection molds foraging behavior to maximize fitness
-maximize fitness by choosing prey that gets more energy in than they put out
Optimality Modeling
Assumes consumers make choices
no necessarily
Assumes consumers make choices
Not Necessarily Conscious
Based on: Recent Experience Physiological State Ability to capture Proximate Feedbacks Search Image
Principle of Allocation
organisms must
Assumes if energy supplies are limited, organisms cannot simultaneously maximize all life functions.
Organisms Must:
-Compromise between competing demands
-Reduce Relative Cost for Foraging
most beneficial are prey that are
intermediate in size
forage on animals that
that have the greatest return
Should predator consume prey item?
energy intake ______ by diet breadth
factors to consider for prey:
-Energy intake optimized by diet breadth
–# of different prey items in diet
Factors
-Prey energy content
-Prey Escape ability
-Prey abundance
search time decreases when
there is more food availability
Prey Model only applies to .
herbivores rather alter
when should a consumer leave a patch
Predators
- Herbivores generally do not alter food choice
- Rather Alter Forage Patches
When should a consumer Leave a Patch?
- Most Prey items occur in patches
- Predators deplete Prey abundance
Patch-use Model
-Central-place Foraging Model
Consumer should leave patch when
profitability of patch < surrounding area
Giving-up time
- Amount of time that a foraging animal stays in a patch before leaving to find another patch
- Balances rate of gain in current patch to travel time (cost) to next profitable patch
- Assumes Animal knows the profitability of surrounding patches ?????
Risk-Sensitive Foraging
risk-averse
risk-prone
Risk-averse
-Individual takes fewer risks but achieves lower net gain
Risk-Prone
-Individual takes more risks but achieves higher net gain
Strategy depends on Needs of Individual
-Chooses Strategy that allows best survival
Gause
Attempted to produce population cycles with P. caudatum and Didinium nasutum.
Gause Attempted to produce population cycles with P. caudatum and Didinium nasutum. Didinium quickly consumed all Paramecium Went extinct -Both populations extinct
To persist in the face of exploitation:
hosts need
Hosts and prey need refuges Gause Added sediment for Paramecium refuge. Didinium went extinct Paramecium thrived initially Eventually went extinct
Must add
stable cycling requires:
refuges and immigration to maintaining long term
what is needed in the system along with immigration and refugee
complexity
Predators & Prey Defense
based on
selective pressures for
prey need to be what to survive predators
- Predators usually selection agents for refined prey defense.
- -Must catch and subdue prey
- -Usually eliminate more conspicuous (less adaptive) members of a population
- Selective pressures for
- -Size
- -Behavior
- -Defensive structures
-prey need to be fit to survive predators
Predator & prey species are engaged in
a co-evolutionary race.
Prey Defenses:
group defense
color defense
cryptic colaration
aposematic coloration
- Group Defense (Flocking)
- -Predator Confusion
- -Group Awareness
Coloration Cryptic Coloration -Blend into background Aposomatic Coloring -Warning colors
Mimicry
- mullerian
- Batesian
-Mullerian mimicry
Comimicry among several –species of noxious organisms.
-Batesian mimicry
–Harmless species mimic noxious species.
Protection in Numbers
Predator satiation defense
-can ____ the ____ of being eaten
- Living in a large group provides a “refuge.”
- Predator’s response to increased prey density:
- Wide variety of organisms employ predator satiation defense.
- Prey can reduce individual probability of being eaten by living in dense populations.
Masting
Janzen
O’Dowd and Gill
Synchronous, widespread seed & fruit production
Proposed that seed predation is a major selective force favoring mast crop production.
Determined synchronous seed dispersal by Eucalyptus reduces losses of seeds to ants.
-drop all at once to make it into the soil
cicadas show
predator satiation
Emerge as adults every 13-17 years.
Densities can approach 4x106 ind / ha.
-brias can’t evolve to take a strategy emergence too long
Size As A Refuge
-If large individuals are ignored by predators
-Large size may offer a form of refuge.
Peckarsky
Observed mayflies (Family Ephenerellidae)
make themselves look larger in the face of foraging stoneflies.
-In terms of optimal foraging theory, large size equates to lower profitability.
increase size lower energy probability
