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Exploitation: Predation, Herbivory, Parasitism, and Disease. Chapter 14. 1. Define terms associated with Exploitation. Exploitation : Interaction between populations that enhances fitness of one individual while reducing fitness of the exploited individual.

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Exploitation: Predation, Herbivory, Parasitism, and Disease

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Exploitation predation herbivory parasitism and disease l.jpg

Exploitation: Predation, Herbivory, Parasitism, and Disease

Chapter 14

1 define terms associated with exploitation l.jpg

1. Define terms associated with Exploitation.

  • Exploitation: Interaction between populations that 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, but do not generally kill the host.

      • Parasitoid is an insect larva that consumes the host.

    • Pathogens induce disease.

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2. Parasites That Alter Host Behavior

  • Spring-Headed Worm (Acanthocephalans) changes behavior of amphipods in ways that make it more likely that infected amphipods will be eaten by a suitable vertebrate host.

    • Infected amphipods swim toward light, which is usually indicative of shallow water, and thus closer to predators.

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Parasites That Alter Host Behavior

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Parasites That Alter Host Behavior

  • Rust fungus Puccinia monoica manipulates growth of host mustard plants (Arabis spp.).

    • Puccinia infects Arabis rosettes and invades actively dividing meristemic tissue.

      • Rosettes rapidly elongate and become topped by a cluster of bright yellow leaves.

        • Pseudo-flowers are fungal structures including sugar-containing spermatial fluids.

          • Attract pollenators

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Parasites That Alter Host Behavior

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3. Entangling Exploitation with Competition

  • Deer + moose Brain worm – moose more affected

  • Moose more competitive in Northwoods except when affected by deer brainworm.

  • Rear leg weakness, Lameness, Ataxia (an uncoordinated gait)

  • Stiffness, Paraplegia, Paralysis, Hypermetria (exaggerated stepping motions)

  • Circling, Abnormal Head Position, Arching of the Neck, Blindness,Gradual Weight Loss

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Deer Brain worm life cycle

  • Parelaphostrongylus tenuis or meningeal worm as it is more commonly known. White-tailed deer are the natural host for the parasite and do not usually have the life threatening form found in other ruminant species. P. tenuis is found everywhere that white-tailed deer are found.

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4. Herbivorous Stream Insect and Its Algal Food – impact of herbivores

  • 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.

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Herbivorous Stream Insect and Its Algal Food

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Impact of herbivores 2

  • Deer enclosure experiments on sapling growth

  • Changes in species number with & without deer

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Impact of white tail deer on trees

  • Number of saplings/acre

  • Species with deer w/o deer

  • Red oak 10.5 11

  • White oak 8.2 6.2

  • Hickory 6.0 5.5

  • Sugar Maple .5 15.0

  • Sassafras 0 8.2

*Be able to draw a graph showing these results on exam 3.

Which species are more affected by deer & why?

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5. 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 pop.Reduced by 3 orders of magnitude in 2 years.

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Exploitation and Abundance

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6. Cycles of Abundance in Snowshoe Hares and Their Predators

  • Snowshoe Hares (Lepus americanus) and Lynx (Lynx canadensis).

    • Extensive trapping records.

    • Elton proposed abundance cycles driven by variation in solar radiation.

    • Keith suggested overpopulation theories:

      • Decimation by disease and parasitism.

      • Physiological stress at high density.

      • Starvation due to reduced food.

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Population Fluctuations

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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.

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Snowshoe Hares - Role of Predators

  • 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.

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    7. Population Cycles in Mathematical and Laboratory Models

    • 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 parasitism / predation.

        • Nh = Number of hosts.

        • Np = Number of parasites / predators.

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    8. 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.

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    Model Behavior

    • Reciprocal effects produce oscillations in two populations.

      • Although the assumptions of eternal oscillations and that neither host nor exploiter populations are subject to carrying capacities are unrealistic, L-V models made valuable contributions to the field.

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    9. Laboratory Models

    • Utida found reciprocal interactions in adzuki bean weevils Callosobruchus chinensis 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.

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    10. Refuges

    • To persist in the face of exploitation, hosts and prey need refuges.

    • Gause attempted to produce population cycles with P. caudatum and Didinium nasutum.

      • Didinium quickly consumed all Paramecium and went extinct. (Both populations extinct)

        • Added sediment for Paramecium refuge.

          • Few Paramecium survived after Didinium extinction.

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    • Huffaker 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 maintained population oscillations spanning 6 months.

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    11. Protection in Numbers

    • Living in a large group provides a “refuge.”

    • Predator’s response to increased prey density:

      Prey consumed x Predators = Prey Consumed


    • Wide variety of organisms employ predator satiation defense.

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

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    11. Masting: Predator Satiation by an Australian Tree

    • Synchronous widespread seed and fruit production is known as masting.

      • 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.

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    12. 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.

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    13. 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.

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