Exploitation: Predation, Herbivory, Parasitism, and Disease - PowerPoint PPT Presentation

Exploitation: Predation, Herbivory, Parasitism, and Disease

Chapter 14

• 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.

• 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.

• 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

• 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

• 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.

• 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.

• Deer enclosure experiments on sapling growth
• Changes in species number with & without deer

• 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?

• 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.

• 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.

• 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.

• 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.

• 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.
• 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.

• 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.

• 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.

• 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.

• 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.

• 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.

• 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.