Lecture 12: Exploitation

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Exploitative interactions

Predation
Herbivory
Parasitism
Disease

Examples

Effects on distribution, abundance and structure of populations

Dynamics

Predator-prey population cycles
Modeling predator-prey dynamics
- Laboratory tests
- Importance of refuges
- Space, numbers size

Exploitation

Interaction where one organism benefits and the other experiences a decrease in growth, reproduction, or survivorship

Predators

Kill prey immediately after attacking them
Consume several or many prey over a lifetime

Herbivores/Grazers

Don’t typically kill prey
Only partially consume individuals
Consume several prey over a lifetime

Parasites

Typically do not kill prey
Only consume part of prey
Attack only one or very few prey over a lifetime

Parasitoids

Kill prey over prolonged period
Young consume most of prey (from inside out)
Attack only one or very few prey in a lifetime
Mainly Hymenoptera and Diptera

Pathogens

Cause disease (debilitation sometimes severely) in hosts

Definitions

Predators: Kill and consume other organisms

Herbivores: Consume prey without killing it

Parasites: Live on host tissue – reduce host fitness. Do not generally kill host

Parasitoids: Lay eggs in host – larvae consumes and kills host.

Pathogens: Diseases

Exploitation

All forms of exploitation result in some form of fitness decrease

Exploitative relationships are complex

Effects of parasites on host behavior

Interactions among predation, parasitism, and competition

Park found the presence/absence of a protozoan parasite (Adeline tribolii) influences competition in flour beetles (Tribolium).
- Adelina lives as an intercellular parasite.
- - Reduces density of T. castaneum but has little effect on T. confusum.
  - T. castaneum is usually the strongest competitor, but with the presence of Adelina, T. confusum becomes strongest competitor.

Introduce Adelina

, a parasite

Herbivorous Stream Insect and Its Algal Food

Lamberti and Resh studied influence of caddisfly (Helicopsyche borealis) on algal and bacterial populations on which it feeds.
- Results suggest larvae reduce the abundance of their food supply.

Exploitation and Abundance

Introduced Cactus and Herbivorous Moth
- Mid 1800’s:prickly pear cactus Opuntia stricta was introduced to Australia

Established populations in the wild
Government asked for assistance in control
Moth Cactoblastis cactorum found to be effective predator
- Reduced by 3 orders of magnitude in 2 years

Exploitation and Abundance

One of the best examples of successful use of biological control

Dynamics

Predator-prey population cycles
Modeling predator-prey dynamics
- Laboratory tests
- Importance of refuges
- - Space, numbers size

Cycles of Abundance in Snowshoe Hares and Their Predators

Hudson’s Bay Company in Manitoba, Canada

Fur trapping records for ~ 200 years (1700s- 1900s)

One of the best datasets demonstrating predator-prey population cycles

Population Fluctuations

What causes these cycles?

Snowshoe Hares - Role of Food Supply

Live in boreal forests dominated by conifers
- Dense growth of understory shrubs
In winter, browse on buds and stems of shrubs and saplings such as aspen and spruce
- One population reduced food biomass from 530 kg/ha in late Nov. to 160 kg/ha in late March
Shoots produced after heavy browsing can increase levels of plant chemical defenses
- Reducing usable food supplies
Lynx (Classic specialist predator)
- Coyotes may also play a large role
Predation can account for 60-98% of mortality during peak densities
Complementary:
- Hare populations increase, causing food supplies to decrease. Starvation and weight loss may lead to increased predation, all of which decrease hare populations

Modeling Predation

Lotka (1925)

Moth and butterfly larvae and parasitoids

Volterra (1926)

Marine fish populations

Lotka-Volterra Model of Predator-Prey Interactions

(Note: same equations for a predator, parasite, or pathogen)

Lotka-Volterra assumes host population grows exponentially, and population size is limited by parasites, pathogens, and predators:

dNh/dt = rhNh – pNhNp

rhNh = exponential growth by host population opposed by:

p = rate of predation (efficiency of predation)
Nh = number of hosts
Np = number of predators

mouse dNp/dt = cpNhNp– dpNp

cat dNh/dt = rhNh – pNhNp

Model Behavior

Host exponential growth often 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

Reciprocal effects produce oscillations in two populations

Assumptions:

Instant conversion of change in one population to change in the other (e.g., predation on prey immediately translated into new predators)
Neither population is subject to K

Still: L-V models made valuable contributions to the field

Laboratory Models

Can we produce L-V population cycles (oscillations) in the lab?

Utida found reciprocal interactions in adzuki bean weevils Callosobruchus chinensis and a parasitoid wasp over several generations.

Gause found similar patterns in P. aurelia
Most laboratory experiments have failed in that most have led to the extinction of one population within a relatively short period.

Can we produce L-V population cycles (oscillations) in the lab?

Yes, but very difficult
How to generate these cycles in the lab to mimic what we see in nature?
- Gause’s paramecium experiments
How to generate these cycles in the lab to mimic what we see in nature?
- Gause’s paramecium experiments
- Refuges!

Refuges

Huffaker (1958) studied six-spotted mite Eotetranychus sexmaculatus and predatory mite Typhlodromus occidentalis

Separated oranges and rubber balls with partial barriers to mite dispersal
Typhlodromus crawls while Eotetranychus balloons
Provision of small wooden posts to serve as launching pads

Types of refuges

Space
Numbers
Size

Protection in Numbers

Living in a large group provides a “refuge.”
Predator’s response to increased prey density

Numerical and functional response
- Level off (limit to increased response) = predator satiation

Prey can reduce individual probability of being eaten by living in dense populations

Masting

Life history characteristic
- the reproductive habit of some tree species where populations produce large seed crops (fruits) synchronously in some years and small seed crops otherwise

Predator Satiation by an Australian Tree

Janzen proposed that seed predation is a major selective force favoring mast crop production.

O’Dowd and Gill determined synchronous seed dispersal by Eucalyptus reduces losses of seeds to ants.

Predator Satiation by Periodical Cicadas

Periodical cicadas Magicicada spp. emerge as adults every 13-17 years

Densities can approach 4x106 ind / ha

Williams estimated 1,063,000 cicadas emerged from 16 ha study site

50% emerged during four consecutive nights
Losses to birds was only 15% of production

Periodical Cicadas

Billions of cicada carcasses

Effects of “resource pulse?”

Added 300 dead cicadas/m2

increased amounts of soil microbes, fungi and soil nitrogen
faster growing trees
bigger seeds in some flowering plants

Size as a Refuge

If large individuals are ignored by predators, then large size may offer a form of refuge.

Peckarsky observed mayflies (Family Ephenerellidae) making themselves look larger in the face of foraging stoneflies.
In terms of optimal foraging theory, large size equates to lower profitability (increased costs of handling/struggling)

Copyright 2008, by the Contributing Authors. Cite/attribute Resource. factpetersen. (2008, March 04). Lecture 12: Exploitation. Retrieved November 23, 2009, from Free Online Course Materials — USU OpenCourseWare Web site: http://ocw.usu.edu/biology/general-ecology/lecture12/lecture-12-exploitation. This work is licensed under a Creative Commons License.

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Lecture 12: Exploitation

Document Actions

Exploitative interactions

Exploitation

Predators

Herbivores/Grazers

Parasites

Parasitoids

Pathogens

Definitions

Exploitation

Herbivorous Stream Insect and Its Algal Food

Exploitation and Abundance

Exploitation and Abundance

Dynamics

Snowshoe Hares - Role of Food Supply

Modeling Predation

Model Behavior

Laboratory Models

Refuges

Protection in Numbers

Masting

Predator Satiation by an Australian Tree

Predator Satiation by Periodical Cicadas

Periodical Cicadas

Size as a Refuge

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	Info Lecture 12: Exploitation Document Actions Contents Exploitative interactions Predation Herbivory Parasitism Disease Examples Effects on distribution, abundance and structure of populations Dynamics Predator-prey population cycles Modeling predator-prey dynamics Laboratory tests Importance of refuges Space, numbers size Exploitation Interaction where one organism benefits and the other experiences a decrease in growth, reproduction, or survivorship Predators Kill prey immediately after attacking them Consume several or many prey over a lifetime Herbivores/Grazers Don’t typically kill prey Only partially consume individuals Consume several prey over a lifetime Parasites Typically do not kill prey Only consume part of prey Attack only one or very few prey over a lifetime Parasitoids Kill prey over prolonged period Young consume most of prey (from inside out) Attack only one or very few prey in a lifetime Mainly Hymenoptera and Diptera Pathogens Cause disease (debilitation sometimes severely) in hosts Definitions Predators: Kill and consume other organisms Herbivores: Consume prey without killing it Parasites: Live on host tissue – reduce host fitness. Do not generally kill host Parasitoids: Lay eggs in host – larvae consumes and kills host. Pathogens: Diseases Exploitation All forms of exploitation result in some form of fitness decrease Exploitative relationships are complex Effects of parasites on host behavior Interactions among predation, parasitism, and competition Park found the presence/absence of a protozoan parasite (Adeline tribolii) influences competition in flour beetles (Tribolium). Adelina lives as an intercellular parasite. Reduces density of T. castaneum but has little effect on T. confusum. T. castaneum is usually the strongest competitor, but with the presence of Adelina, T. confusum becomes strongest competitor. Introduce Adelina , a parasite Herbivorous Stream Insect and Its Algal Food Lamberti and Resh studied influence of caddisfly (Helicopsyche borealis) on algal and bacterial populations on which it feeds. Results suggest larvae reduce the abundance of their food supply. Exploitation and Abundance Introduced Cactus and Herbivorous Moth Mid 1800’s:prickly pear cactus Opuntia stricta was introduced to Australia Established populations in the wild Government asked for assistance in control Moth Cactoblastis cactorum found to be effective predator Reduced by 3 orders of magnitude in 2 years Exploitation and Abundance One of the best examples of successful use of biological control Dynamics Predator-prey population cycles Modeling predator-prey dynamics Laboratory tests Importance of refuges Space, numbers size Cycles of Abundance in Snowshoe Hares and Their Predators Hudson’s Bay Company in Manitoba, Canada Fur trapping records for ~ 200 years (1700s- 1900s) One of the best datasets demonstrating predator-prey population cycles Population Fluctuations What causes these cycles? Snowshoe Hares - Role of Food Supply Live in boreal forests dominated by conifers Dense growth of understory shrubs In winter, browse on buds and stems of shrubs and saplings such as aspen and spruce One population reduced food biomass from 530 kg/ha in late Nov. to 160 kg/ha in late March Shoots produced after heavy browsing can increase levels of plant chemical defenses Reducing usable food supplies Lynx (Classic specialist predator) Coyotes may also play a large role Predation can account for 60-98% of mortality during peak densities Complementary: Hare populations increase, causing food supplies to decrease. Starvation and weight loss may lead to increased predation, all of which decrease hare populations Modeling Predation Lotka (1925) Moth and butterfly larvae and parasitoids Volterra (1926) Marine fish populations Lotka-Volterra Model of Predator-Prey Interactions (Note: same equations for a predator, parasite, or pathogen) Lotka-Volterra assumes host population grows exponentially, and population size is limited by parasites, pathogens, and predators: dNh/dt = rhNh – pNhNp rhNh = exponential growth by host population opposed by: p = rate of predation (efficiency of predation) Nh = number of hosts Np = number of predators mouse dNp/dt = cpNhNp– dpNp cat dNh/dt = rhNh – pNhNp Model Behavior Host exponential growth often 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 Reciprocal effects produce oscillations in two populations Assumptions: Instant conversion of change in one population to change in the other (e.g., predation on prey immediately translated into new predators) Neither population is subject to K Still: L-V models made valuable contributions to the field Laboratory Models Can we produce L-V population cycles (oscillations) in the lab? Utida found reciprocal interactions in adzuki bean weevils Callosobruchus chinensis and a parasitoid wasp over several generations. Gause found similar patterns in P. aurelia Most laboratory experiments have failed in that most have led to the extinction of one population within a relatively short period. Can we produce L-V population cycles (oscillations) in the lab? Yes, but very difficult How to generate these cycles in the lab to mimic what we see in nature? Gause’s paramecium experiments How to generate these cycles in the lab to mimic what we see in nature? Gause’s paramecium experiments Refuges! Refuges Huffaker (1958) studied six-spotted mite Eotetranychus sexmaculatus and predatory mite Typhlodromus occidentalis . Separated oranges and rubber balls with partial barriers to mite dispersal Typhlodromus crawls while Eotetranychus balloons Provision of small wooden posts to serve as launching pads Types of refuges Space Numbers Size Protection in Numbers Living in a large group provides a “refuge.” Predator’s response to increased prey density Numerical and functional response Level off (limit to increased response) = predator satiation Prey can reduce individual probability of being eaten by living in dense populations Masting Life history characteristic the reproductive habit of some tree species where populations produce large seed crops (fruits) synchronously in some years and small seed crops otherwise Predator Satiation by an Australian Tree Janzen proposed that seed predation is a major selective force favoring mast crop production. O’Dowd and Gill determined synchronous seed dispersal by Eucalyptus reduces losses of seeds to ants. Predator Satiation by Periodical Cicadas Periodical cicadas Magicicada spp. emerge as adults every 13-17 years Densities can approach 4x106 ind / ha Williams estimated 1,063,000 cicadas emerged from 16 ha study site 50% emerged during four consecutive nights Losses to birds was only 15% of production Periodical Cicadas Billions of cicada carcasses Effects of “resource pulse?” Added 300 dead cicadas/m2 increased amounts of soil microbes, fungi and soil nitrogen faster growing trees bigger seeds in some flowering plants Size as a Refuge If large individuals are ignored by predators, then large size may offer a form of refuge. Peckarsky observed mayflies (Family Ephenerellidae) making themselves look larger in the face of foraging stoneflies. In terms of optimal foraging theory, large size equates to lower profitability (increased costs of handling/struggling) Copyright 2008, by the Contributing Authors. Cite/attribute Resource. factpetersen. (2008, March 04). Lecture 12: Exploitation. Retrieved November 23, 2009, from Free Online Course Materials — USU OpenCourseWare Web site: http://ocw.usu.edu/biology/general-ecology/lecture12/lecture-12-exploitation. This work is licensed under a Creative Commons License.