Exploitation: Predation, Herbivory, Parasitism, and Disease Chapter 14 1

Introduction • Exploitation : Interaction between populations that enhances fitness of one individual while reducing fitness of the exploited individual.

 Predators (herbivores or carnivores) kill and consume other organisms.

 Parasites live on host tissue and reduce host fitness, but do not generally kill the host.

 Pathogens cause infectious disease.

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Overview: • Prey defense adaptations • Parasites Effects • Predator-Prey Cycles • Refuges and immigration for persistence.

• Predator Satiation • Biocontrol 3

Figure 53.5 Camouflage: Poor-will (left), lizard (right)

Camouflage

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Mullerian mimic (wasp) Batesian mimic (fly) 5

“Predation” on plants - herbivory • Physical defenses  Thorns, silica • Chemical defenses  Toxins and tastes  Alkaloids (very diverse)  Polyphenolics (tannins) 6

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Parasites

• • • • • • Parasites can have multiple developmental stages, each with its own host.

Parasitoid: larvae develops in host (e.g. wasps) Parasitism can be based in parasite behavior.

Parasite infection can modify host behavior for the benefit of the parasite.

Parasites can change competition outcomes of host and its competitor.

Parasites of predators can benefit prey.

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Schistosoma Life Cycle 10

Figure 53.x2 Parasitic behavior: A female

Nasonia vitripennis

laying a clutch of eggs into the pupa of a blowfly (

Phormia regina

) 11

Brood Parasitism

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Momma wood thrush has fallen for all babies being cute.

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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 15

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 16

Parasites That Alter Host Behavior 17

Entangling Exploitation with Competition •

Park

found the presence/absence of a protozoan parasite (

Adeline tribolii

) influences competition in flour beetles (

Tribolium

).

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Entangling Exploitation with Competition 

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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Predation Influenced by Disease (Lindstrom et al., 1994) 21

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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 disease and parasitism.

 Physiological stress at high density.

 Starvation due to reduced food.

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Population Fluctuations 24

• • Snowshoe Hares – Observational Evidence Food - 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.

Predators -Lynx (Classic specialist predator)  Coyotes may also play a large role.

 Predation can account for 60-98% of mortality during peak densities.

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Snowshoe Hares – Experimental Evidence • 3 control plots, 6 experimental plots  Added food (2) or fertilizer (2) or removed predators (2) • Predator removal and food supplementation increased hare density 26

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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: dN h /d t = r h N h – pN h N p r h N h = Exponential growth by host population.

 Opposed by:  p = rate of parasitism or predation.

 N h = Number of hosts.

 N p = Number of parasites or predators.

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Population Cycles in Mathematical and Laboratory Models • • • • • Lotka Volterra assumes parasite/predator growth rate is determined by rate of conversion of food into host offspring minus mortality rate of parasitoid population: dN p /d t = cpN h N p -d p N p cpN h N p = predator rate of production from exploited hosts.

pN h N p hosts.

= Rate at which predators consume c = Conversion factor (host to predator) d = Death rate of predator.

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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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Wasp and Weevil 33

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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Refuges and Immigration 35

Size As A Refuge • If large individuals are ignored by predators, then large size may offer a form of refuge.

 Many predators are gape-limited – they cannot open their mouths wide enough to capture prey larger than a certain size 36

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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Predator Satiation by Periodical Cicadas • • Periodical cicadas

Magicicada spp

. emerge as adults every 13-17 years.

 Densities can approach 4x10 6 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.

http://news.nationalgeographic.com/news/2004/03/0329_040329_cicadas.ht

ml#main Cicadas in PA 38

Biocontrol of Unwanted Species • 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.

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Exploitation and Abundance 40

Biocontrol

• • • Use of one or more beneficial organisms to control pests  Classical – introduce predator from pest’s original country  Inoculative – release of natural enemies  Innundative – Mass-releases of natural enemies Predators, parasitoids, pathogens, herbivores http://www.nysaes.cornell.edu/ent/biocontrol/ 41