BIOS 3010: Ecology Lecture 7: Processes: Predation • 1. Lecture summary: – Horizontal & vertical interactions.
– Vertical Henri Rousseau, The sleeping gypsy” 1897, MMA, New York interactions:
– Predation:
• Classifications
• Defense
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2. The basic nature of interactions within and between trophic levels: • Horizontal interactions within a trophic level: – competition > amensalism > commensalism > mutualism • Vertical interactions between trophic levels: – Predation / parasitism / herbivory > mutualism Malcolm (1992)
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3. Summary of ecological interactions:
Interaction Species 1 Species 2 a) Horizontal competition - - amensalism - 0 commensalism 0 + mutualism + +
b) Vertical predation - + parasitism - + herbivory - + mutualism + +
• NB neutralism is really an irrelevant 0/0 interaction; and it is also important to realize that herbivores are usually the prey or hosts for predators and parasites
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1 4. Vertical trophic interactions can be divided into two basic kinds:
• (1) Consumers that do not kill their food – these are the parasites which include pathogens and herbivores - neither of which completely consume their food hosts.
• (2) Consumers that do kill their food – these are the predators which include typical animal predators as well as insectivorous plants and seed-eating animals like birds, small mammals and insects.
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5. Predation:
• Predation is a +/- or “exploitative” interaction between consumers and the things they consume. – Consumers affect the distribution and abundance of what they consume and vice versa.
• Predation is consumption of one organism (the prey) by another organism (the predator), in which the prey is alive when the predator first attacks it. – This excludes detritivory as feeding on dead organic matter
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6. Predation
• Taxonomic classification (trivial):
– Carnivores consume animals.
– Herbivores consume plants.
– Omnivores consume both plants and animals.
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2 7. Predation
• Functional classification: • True predators: – kill and consume prey immediately; kill many prey. – like lions and seed-eating beetles. • Grazers: – attack many "prey"; rarely lethal; only partially consume. – like sheep and mosquitoes. • Parasites: – attack few or single "prey"; rarely lethal; only partially consume. – micro & macroparasites - measles, tapeworms, gall wasps & aphids. • Parasitoids: – attack single "prey", always lethal, complete consumption. • This is why Begon et al. (2006) consider herbivory as a subset of predation - mostly as plant grazers, but also as plant parasites. • Because there are important differences between predators and herbivores, herbivory will be considered in more detail in lecture 11!
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8. The effect of predation on prey populations:
• Predators should be harmful to prey populations because they attack and kill individual prey, but this may not be true for 2 reasons: – 1) killed individuals may not be a random sample of the population and may be those with lowest fitness (old, young or sick individuals) see Fig. 9.9. – 2) there may be compensatory changes in growth, survival or reproduction of surviving prey. • e.g. recruitment curves in Fig. 5.10b indicate that predation of high density individuals should lead to increased growth and reproduction - but at low density the effect could be reversed (this influences resource harvesting)
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9. Prey as food resources for Predators:
• Increased food consumption leads to increased rates of growth, development & birth, and decreased rates of mortality - above a metabolic maintenance threshold and below a satiation threshold – Fig. 8.10 (3rd ed.) (a) Linyphiid spider (b) Daphnia water flea.
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3 10. Prey defense:
• Predator satiation: – Predator satiation suggests that some prey may target this as a defense against being consumed - and so they evolve mechanisms to synchronize their peak periods of population abundance: • Like periodical cicadas (Magicicada) in which there are twelve, 17-year and three, 13-year broods currently in existence in eastern North America: – see cover, Table 1 and Fig. 1 from Heliövaara et al. 1994,Trends in Ecology & Evolution 9(12): 476
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11. Prey defense:
• Masting: • Fruit/seed masting in trees (Fig. 8.11), and inverse density dependence in Fig. 8.12 to show that predators may not track prey food resources when they fluctuate (Fig. 9.12) unless they have short generation times. • Nutritional quality: • Prey may reduce their nutritional quality by dilution or other means such as toxins or digestibility-reducing chemicals. • see protein availability for wildebeest in Fig. 9.13 - which argues for predator foraging behaviors; to be considered next time ...…
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Figure 9.9: Age classes of Thomson’s gazelles lost to predators in the Serengeti
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4 Figure 5.10b: Clover growth rate against leaf area index at different light intensities
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Trends in Ecology & Evolution (1994) Vol. 9(12)
Periodical cicadas in the genus Magicicada form a complex of 6 species each with 13-year and 17-year life cycles. Broods X & XIX are separated by mtDNA genotypes in Fig. 3 below
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Table 1: (Heliövaara et al. 1994, TREE 9(12):476
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5 Figure 1: Heliövaara et al. 1994, TREE 9(12):478
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Figure 8.11 (3rd ed.): Periodical masting in Scots pine and Norway spruce
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Figure 8.12 (3rd ed.): Inverse density depen- dence in weevil attacks on witch hazel fruits
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6 Figure 9.12: Inverse plant and mirid bug numbers in the Negev desert
Asphodelus fruits
nymphs
adults
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Figure 9.13: Wildebeeste food quality and bone marrow fat in the Serengeti
Live males Eaten protein
Dead males
Available protein
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