1. Predation, Herbivory, and Parasitism

2. Types of Species Interactions  When two species interact, the effects for each species can be positive, negative, or neutral.  Competition -/-  Amensalism -/0  Commensalism +/0  Mutualism +/+  Exploitation +/-

3. Types of Species Interactions  Exploitative interactions include:  Predation  Herbivory  Parasitism

4. Parasitism  Parasites live in or on their host's body and often spend most or all their lives eating tissues or body fluids of just one host individual.  Sometimes multiple generations of parasites live on the same host.  Because parasites depend on their hosts for continued feeding, they do not generally kill their hosts (at least not immediately).

5. Parasitism  Most parasites associated with a single host species have a free-living life stage during which they are not attached to a host.  A great many other parasites, though, have multiple hosts with different life stages adapted to each host (and possibly free-living stages as well).

6. Endoparasites  The inside of an organism is a much more stable and protected environment than the outside, and endoparasites (e ndo = inner) take advantage of this by living and feeding inside their hosts

7. Ectoparasites  Although parasites tend to be tiny and hard to see, ectoparasites (ecto=outer), which live on the outside surface of their host, are often easier to observe.

8. Ectoparasites  By living outside their host, ectoparasites avoid having to defend themselves against the host's immune system.  The trade-off, however, is that they are exposed to predation and a sometimes harsh exterior environment.  Some species of predators specialize on ectoparasites.

9. Ectoparasites  The cleaner wrasse is a type of fish that lives in coral reefs.  Other fish will wait patiently while a cleaner fish picks off parasites from their scales, mouth, and gills.

10. Parasitoids and Hyperparasites  Most of the parasites discussed so far do not directly kill their hosts but, parasitoids do.  Parasitoids develop inside their host and essentially eat it from the inside out.  When the host is completely consumed, the parasitoid transforms into an adult and crawls out to find new hosts for its offspring.

11. Parasitoids and Hyperparasites  Interestingly, the parasitoid wasp has a parasitoid of its own, known as a secondary parasitoid, or hyperparasitoid.  Hyperparasitoid wasps find aphids with internal parasitoid larvae and lay eggs inside the larvae.

12. Ecological Impacts of Parasites  Parasites can have broad ecological impacts.  These effects begin at the individual level; because parasites rob their hosts of resources, host survival and/or reproduction can be reduced even when hosts are not killed by parasites directly.

13. Effects of Parasites on Individual Hosts  A protozoan causes rats to become attracted to cats.  A nematode turns the bellies of Amazonian ants red, attracting berry-eating birds.  A fluke makes ants climb grass stems so they will be eaten by sheep.  A trematode causes killifish to swim closer to the surface of the water, making them easy targets for birds.

14. Herbivores  Grazers are herbivores that specialize on herbaceous plants (grasses, forbs, and herbs), while browsers eat the leaves, bark, and twigs of woody plants.  Herbivores that specialize on seeds are granivores, while those specializing on fruits are frugivores.

15. Plant Defenses Against Herbivory  Herbivory is generally not a positive experience for a plant, so plants have evolved forms of self-defense.  Mechanical - Developing structures like thorns that make it harder for animals to eat them.  Chemical - Producing chemicals that are noxious or poisonous to herbivores.  Nutritional - Growing structures that are less nutritious for grazers (have less N and P).  Tolerance - Adaptions to regrow quickly after being grazed.

16. Impacts of Herbivory on Plant Communities  Herbivory can reduce the overall number of plants and can also have a profound impact on the composition of a plant community.

17. Impacts of Herbivory on Plant Communities  When plants have evolved without selective pressure from herbivory, they may not be very well-defended, and the influence of herbivores can be even more drastic.  This is a problem when new herbivores are introduced.

18. Predation  Lynx are fast, but lack endurance, so they don't chase hares over long distances.  Instead, they stalk hares, hiding behind trees and brush until they can get close enough to pounce on a hare.

19. Predation  Stalking is one of a variety of strategies used by predators for catching mobile prey.  Others include pursuit, where the predator chases prey over a distance; ambush, where the predator hides and waits in one spot until prey comes along; and random encounter, where the predator and prey meet by chance.

20. Animal Defenses Against Predation  Just as plants have evolved defense mechanisms to combat herbivory, animals have evolved ways to defend themselves from predation.  Chemical - Producing chemicals that are noxious or poisonous to predators.  Physical - Developing physical barriers to predation (e.g., shells).  Behavioral - Behaving in ways that minimize risk from predation.

21. Animal Defenses Against Predation  Aposematism - Warning colors, sounds, or other characteristics to alert predators that this prey will not be tasty.  Crypsis - Camouflaged colors, shapes, and other ways of hiding from predators.  Mimicry - Looking, sounding, or in other ways mimicking a species that predators avoid.

22. Predator-Prey Dynamics  Lynx & Snowshoe hare population size records available back to 1800s.  Fur traders  Populations of lynx and hare seemed to follow an interesting cyclic pattern.  Both species peak and then sharply decline about every ten years, at slightly non-overlapping intervals.

23. Prey Dynamics: Modeling Hare  Scientists often use computer models to investigate how different underlying mechanisms might produce particular dynamics in systems.

24. Cycling and Extinction  As the prey population size drops from predation, the predators have less and less food to eat, causing the predator population size to drop.  With fewer predators, the prey population starts growing again, and the cycle repeats.

25. Interactions among Trophic Levels  Predators do not act alone in determining whether prey populations can survive.  Prey can also be strongly affected by the availability and quality of their food.

26. Deterministic vs. Stochastic  The deterministic Lotka-Volterra predator- prey model predicts regular, even cycles of predator and prey populations, with predator cycles following prey cycles.  More realistic models that include chance ( stochastic ) events show variation in both the period and amplitude of predator- prey cycles.