Exploitation: Predation, Herbivory, Parasitism, and Disease

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

2. 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.

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

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

5. Mullerian mimic (wasp) Batesian mimic (fly)

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

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9. 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.

10. Schistosoma Life Cycle

11. Figure 53.x2 Parasitic behavior: A female Nasonia vitripennis laying a clutch of eggs into the pupa of a blowfly (Phormia regina)

12. Brood Parasitism

13. Momma wood thrush has fallen for all babies being cute.

14. 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.

15. Parasites That Alter Host Behavior

16. 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

17. Parasites That Alter Host Behavior

18. Entangling Exploitation with Competition • Park found the presence/absence of a protozoan parasite (Adeline tribolii) influences competition in flour beetles (Tribolium).

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

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23. 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.

24. Population Fluctuations

25. 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.

26. 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

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28. 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 or predation. • Nh = Number of hosts. • Np = Number of parasites or predators.

29. 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: dNp/dt = cpNhNp-dpNp • cpNhNp = predator rate of production from exploited hosts. • pNhNp = Rate at which predators consume hosts. • c = Conversion factor (host to predator) • d = Death rate of predator.

30. 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.

31. 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.

33. Wasp and Weevil

34. 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.

35. Refuges and Immigration

36. 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

37. 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.

38. 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. • http://news.nationalgeographic.com/news/2004/03/0329_040329_cicadas.html#main Cicadas in PA

39. 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.

40. Exploitation and Abundance

41. 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/