•
–   Horizontal & vertical interactions.
–   Vertical interactions:
–   Predation:
•   Classifications
•   Defense
Henri Rousseau, The sleeping gypsy ” 1897, MMA, New York
Dr. S. Malcolm BIOS 3010: Ecology Lecture 7: slide 1
•   Horizontal interactions within a trophic level:
–   competition > amensalism > commensalism > mutualism
•   Vertical interactions between trophic levels:
–   Predation / parasitism / herbivory > mutualism
Dr. S. Malcolm BIOS 3010: Ecology
Malcolm (1992)
Lecture 7: slide 2
Interaction a) Horizontal competition amensalism commensalism mutualism
Species 1
-
-
0
+ b) Vertical predation parasitism herbivory mutualism
-
-
-
+
Species 2
-
0
+
+
+
+
+
+
•   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
Dr. S. Malcolm BIOS 3010: Ecology Lecture 7: slide 3
1

•   (1)
–   these are the parasites which include pathogens and herbivores - neither of which completely consume their food hosts.
•   (2)
–   these are the predators which include typical animal predators as well as insectivorous plants and seed-eating animals like birds, small mammals and insects.
Dr. S. Malcolm BIOS 3010: Ecology Lecture 7: slide 4
•   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
Dr. S. Malcolm BIOS 3010: Ecology Lecture 7: slide 5
•
–   Carnivores consume animals.
–   Herbivores consume plants.
–   Omnivores consume both plants and animals.
Dr. S. Malcolm BIOS 3010: Ecology Lecture 7: slide 6
2

•   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!
Dr. S. Malcolm BIOS 3010: Ecology Lecture 7: slide 7
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)
Dr. S. Malcolm BIOS 3010: Ecology Lecture 7: slide 8
•   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 (3r d ed.) (a) Linyphiid spider (b) Daphnia water flea.
Dr. S. Malcolm BIOS 3010: Ecology Lecture 7: slide 9
3

•
–   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
Dr. S. Malcolm BIOS 3010: Ecology Lecture 7: slide 10
•
•   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.
•
•   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 ...
…
Dr. S. Malcolm BIOS 3010: Ecology Lecture 7: slide 11
Figure 9.9: Age classes of Thomson ʼ s gazelles lost to predators in the Serengeti
Dr. S. Malcolm BIOS 3010: Ecology Lecture 7: slide 12
4

Figure 5.10b: Clover growth rate against leaf area index at different light intensities
Dr. S. Malcolm BIOS 3010: Ecology Lecture 7: slide 13
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
Dr. S. Malcolm BIOS 3010: Ecology Lecture 7: slide 14
Table 1: (Heliövaara et al.
1994, TREE 9(12):476
Dr. S. Malcolm BIOS 3010: Ecology Lecture 7: slide 15
5

Figure 1: Heliövaara et al.
1994, TREE 9(12):478
Dr. S. Malcolm BIOS 3010: Ecology Lecture 7: slide 16
Figure 8.11 (3 rd ed.) : Periodical masting in
Scots pine and Norway spruce
Dr. S. Malcolm BIOS 3010: Ecology Lecture 7: slide 17
Figure 8.12 (3 rd ed.) : Inverse density dependence in weevil attacks on witch hazel fruits
Dr. S. Malcolm BIOS 3010: Ecology Lecture 7: slide 18
6

Figure 9.12: Inverse plant and mirid bug
numbers in the Negev desert
Asphodelus fruits nymphs adults
Dr. S. Malcolm BIOS 3010: Ecology Lecture 7: slide 19
Figure 9.13: Wildebeeste food quality and
bone marrow fat in the Serengeti
Eaten protein
Live males
Dead males
Dr. S. Malcolm
Available protein
BIOS 3010: Ecology Lecture 7: slide 20
7