1. Community Interactions
Principles of Ecology

2. Learning Targets
Compare and contrast symbiotic relationships such as mutualism, commensalism, and parasitism. Identify what effect the relationship has on each species involved.
Use actual examples from nature to explain how interspecific interactions can lead to coevolution.
Explain, with examples, why two species cannot share the same ecological niche (the competitive exclusion principle).
Identify some specific adaptations (camouflage, mimicry, etc.) that have evolved to decrease a species’ chance of being eaten by a predator. Describe the interspecific interactions that must have been in place for the natural selection of these adaptations to occur.

3. Community Ecology
A biological community is an assemblage of populations of various species living close enough for potential interaction.
What are the potential specific community interactions in the photo on the left?
What are the potential specific community interactions in the photo on the right?

4. Community Interactions
Watch the Battle at Kruger.
What interspecific and intraspecific interactions do you observe within this biological community?

5. Interspecific Interactions
Interspecific interactions can have differing effects on the populations involved. Also called Symbiotic Relationships.
Over time, symbiotic relationships may lead to the coevolution of the species involved in the interactions.
Can you think of specific and real examples of each of these interactions?

6. Cattle Egrets (Bubulcus ibis) and Water Buffalo (Bubalus bubalis)
Commensalism
In commensalism one species benefits and the other is not affected.
True commensal interactions have been difficult to document in nature because any close association between species likely affects both species.
Cattle Egrets (Bubulcus ibis) and Water Buffalo (Bubalus bubalis)
The Egrets (white birds in the picture) accompany the water buffalo as they wander. The water buffalo stir up insects in the grass that the egrets eat.
This is an example of a commensalism. Which species is benefiting and which species is neither benefiting nor being harmed?

7. Mutualism
Mutualistic symbiosis, or mutualism is an interspecific interaction that benefits both species.
For example, the acacia (Acacia collinsii) provides sugars for stinging ants (Crematogaster mimosae) and the aggressive ants protect the acacia from herbivory and other insects.
Watch this two minute video (the video links in this PowerPoint are very light in color).
Find the teleological explanation in the video!

8. Termites! The Epitome of Mutualism
As another example, the lower termites (Insecta, Isoptera) provide a gut habitat and food for hundreds of bacterial symbionts and dozens of protozoans in their guts that aid in the digestion of wood compounds and in turn provide acetate to the termite for cellular respiration.
Another interesting (although strange) video that explains the symbiotic relationship between termites and the microorganisms that live in their gut.

9. Ecological Niches
The ecological niche is the total of an organism’s use of the biotic and abiotic resources in its environment.
Two species cannot coexist in a community if their niches are identical.
However, ecologically similar species can coexist in a community if there are one or more significant differences in their niches.
What is different about the niches of the two oystercatchers?

10. Competitive Interactions
Interspecific competition occurs when species compete for a particular resource that is in short supply.
Strong competition can lead to competitive exclusion: the local elimination of one of the two competing species.
Competitive exclusion occurs when two species try to occupy the same niche.
Paramecium caudatum and Paramecium aurelia are similar species that require similar resources (same niches). “A” shows the growth of each population over time if grown separately from each other. “B” shows growth of both species if grown together. How does this demonstrate the competitive exclusion principle?
Fig. 46-6, p. 821

11. The Competitive Exclusion Principle
The competitive exclusion principle states that two species competing for the same limiting resources cannot coexist in the same place (cannot occupy the same niche).
Florida Anole Lizards example: Competitive exclusion and rapid evolutionary change.
Natural selection favors individuals that utilize resources in ways that limits competition. Read some interesting information at the following evolution blog about the Florida Anole Lizards and rapid evolutionary change.

12. Ecological Niches and Resource Partitioning
Individuals with similar (but not identical) niches can coexist though resource partitioning.
Overlapping niches: these three species of plants require similar resources (sun, water, nutrients from the soil), but have evolved over time to coexist with each other without occupying the same niche. What differences in their traits can you observe that allow them to do so?
Fig. 46-8, p. 821
Three annual plant species that have adapted their taproot systems to reduce competition for water and soil minerals. This way they can live together in the same abandoned field 12

13. Other Interspecific Interactions: Predation
Predation refers to an interaction where one species, the predator, kills and eats the other, the prey.
Fig. 46-9, p. 822
Arctic Wolf (Canis lupus arctos)
How do you think the wolf and caribou populations change over many generations of living in the same area? 13

14. Coevolution of Predator and Prey
Cryptic coloration, or camouflage makes prey difficult to spot.
The image on the left looks is an obvious example of camouflage. The least bittern (bird on the right) is not as obviously colored to camouflage in its environment, but it stretches it’s neck upward and sways along with the reeds in the wind when it feels threatened. List two more specific examples of structural and behavioral adaptations.

15. Prey Morphology and Predation Avoidance
Warning coloration warns predators to stay away from prey.
Many predators have probably learned a tough lesson, which causes them to stay away from certain bright colors and patterns. Describe two more examples of warning coloration.

16. Mimicry and Predation Avoidance
In some cases, one prey species may gain significant protection by mimicking the appearance of another.
A palatable or harmless species can evolve to mimic an unpalatable or harmful model.
Which one is the model and which ones are the mimics?
This combination of colors has successfully deterred all kinds of predators, although only one of these species actually has a dangerous sting. The others benefit from the protection provided by the warning colors without having to spend the energy required to be a stinging species. Can you think of another example of model and mimic in nature?

17. Mimicry and Predation Avoidance
In some cases, one prey species may gain significant protection by mimicking the appearance of another.
A palatable or harmless species can evolve to mimic an unpalatable or harmful model.
Nonstinging wasp
This combination of colors has successfully deterred all kinds of predators, although only one of these species actually has a dangerous sting. The others benefit from the protection provided by the warning colors without having to spend the energy required to be a stinging species. Can you think of another example of model and mimic in nature?

18. Herbivory
Herbivory, the process in which an herbivore eats parts of a plant. This has led to the evolution of plant mechanical and chemical defenses and consequent adaptations by herbivores.
Chemical defense
Structural defense
Thorns on the honey locust tree evolved in a time period when protection against grazing from megafauna was an adaptive trait. Thorns are an example of a structural defense against herbivores. What herbivores were present during the evolution of these thorns?
Plants also develop chemical defenses to herbivory. The poison oak on the right would be quite uncomfortable to eat. What are the costs of these defense adaptations? 18

19. Trout with whirling disease
Parasitism
In parasitism, one organism, the parasite, derives its nourishment from another organism, its host, which is harmed in the process, but not usually killed.
Strangleweed
Trout with whirling disease
Protist that causes it
???
Strangleweed – some species produce small amounts of chlorophyll, but some species of strangleweed are not longer photosynthetic. They live entirely off of other plants.
The bottom right picture shows parasites (worms) inside a pig’s intestines. Can you list two other examples of host-parasite interactions? 19

20. Parasitoidism
In parasitoidism, the goal is to use the host temporarily as a home and nutrition source. The host almost always dies. Slightly terrifying and somewhat disgusting parasitoid video.
Braconid wasp laying eggs in caterpillar
Geometrid caterpillar (moth larvae) with Braconid larvae emerging
Parasitoids lay eggs in their hosts. The larvae use the host as a food source. Unlike parasitism, with parasitoidism, the host almost always dies.
The link below will connect you to a quick video on parasatoids. (Warning – it is kind of disgusting, but terribly fascinating).

21. Parasitoidism as a Biological Control
Nests of invasive fire ants
Introduced parasitoid fly
Fire ant casualty
What happened to its head?
Fire ants are an exotic (non-native species), which have taken over certain areas. The solution to this problem? The introduction of a parasitoid fly, which controls fire ant populations in their native environment. The fly lays its eggs in the body of the ant. The larvae hatches and eats its way up the head. When it reaches the head, it releases enzymes which cause the head to fall off of the body of the ant. Now the larvae has a safe and nutrient-full environment to continue growing until it “hatches” from the ant head.
Phorid fly (Pseudacteon sp.): ant-decapitating fly 21

22. The Evolutionary Arms Race: an example
Sonar-jamming Tiger Moths
Click on the link to watch the video. The slide must be in slide –show mode for the link to work, or click on the link below. What is meant by “An evolutionary arms race”? 22

23. Discussion Question
At your table groups, discuss at least 6 different examples of coevolution from the lesson.
What type of interspecific interaction led to the coevolution?
What sort of selective pressure did each species involved in the interaction force upon the other species?