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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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1 define terms associated with exploitation
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.
2 parasites that alter host behavior
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.
parasites that alter host behavior5
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
3 entangling exploitation with competition
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
deer brain worm life cycle
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.
4 herbivorous stream insect and its algal food impact of herbivores
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.
impact of herbivores 2
Impact of herbivores 2
  • Deer enclosure experiments on sapling growth
  • Changes in species number with & without deer
impact of white tail deer on trees
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?

5 exploitation and abundance
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.
6 cycles of abundance in snowshoe hares and their predators
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.
snowshoe hares role of food supply
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.
snowshoe hares role of predators
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.
7 population cycles in mathematical and laboratory models
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.
8 model behavior
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.
model behavior
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.
9 laboratory models
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.
10 refuges
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.
  • 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.
11 protection in numbers
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

Predator Area Area

  • Wide variety of organisms employ predator satiation defense.
    • Prey can reduce individual probability of being eaten by living in dense populations.
11 masting predator satiation by an australian tree
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.
12 predator satiation by periodical cicadas
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.
13 size as a refuge
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.