Exploitation: Predation, Herbivory, Parasitism, and Disease

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Exploitation Predation, Herbivory, Parasitism,
and Disease

• Chapter 14

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Introduction

• _________________ Interaction between
  populations that enhances fitness of one
  individual while reducing fitness of the
  exploited individual.
• ___________ is an insect larva that consumes the
  host.

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Parasites That Alter Host Behavior

• Spring-Headed Worm (Acanthocephalans) changes
  behavior of amphipods in ways that make it more
  likely
• Infected amphipods swim toward light, which is
  usually indicative of shallow water, and thus

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Parasites That Alter Host Behavior
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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 ________________________.
• 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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Entangling Exploitation with 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.

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Exploitation and Abundance

• Introduced Cactus and Herbivorous Moth
• Mid 1800sprickly 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.

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Exploitation and Abundance
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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
• ____________________________ at high density.
• _____________ 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.
• _______________ 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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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
• Nh
• Np

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Model Behavior

• Host exponential growth often opposed by
  _________________.
• Host reproduction immediately translated into
• Increased predation
• More predators
• Larger predator population eventually reduces
  host population, in turn reducing

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Refuges

• To persist in the face of exploitation, hosts and
  prey need
• 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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Other kinds of Refuge?
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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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Protection in Numbers

• Predators response to increased prey density
• Prey consumed x Predators Prey Consumed
• Wide variety of organisms employ
• Prey can reduce

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Size As A Refuge

• If large individuals are ignored by predators,
  then ....
• Peckarsky observed mayflies (Family
  Ephenerellidae) making themselves look larger in
  the face of foraging stoneflies.
• In terms of optimal foraging theory

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