1. Species Interactions
Section 4-2 (p )

2. SYMBIOTIC RELATIONSHIPS
“living together”
a close interaction between organisms of different species for an extended time
although one species always benefits in symbiotic relationships, the secondary species may by harmed, unaffected, OR benefited

3. Species Interactions
There are five major types of symbiotic relationships:
predation
parasitism
competition
mutualism
commensalism

4. PREDATOR – PREY RELATIONSHIPS

5. Coevolution of Predators and Prey
In order to survive, predators must capture and eat prey, while prey must avoid becoming a meal for predators. Therefore, predator and prey populations tend to exert intense selective pressure on one another.
Selective pressures have led to general trends in both predators and prey:
1. increased keenness of senses
2. offensive traits; dentitions, claws, beaks, etc.
3. defensive traits; horns, chemical warfare, speed, camouflage, mimicry, warning coloration, etc.

6. Predation
Predation is a relationship where one organism captures and consumes another.
predator – organism doing the capturing
prey – organism being captured
A predator’s survival depends on its ability to catch its prey.
ie. rattlesnake venom, spider web, etc.
A prey’s survival depends on its ability to avoid being caught.
ie. camouflage, mimicry, physical/chemical defenses

7. Coevolution – MIMICRY
Startle coloration is noted if evolved patterns of color closely resemble the eyes of a much larger animal.
Once warning coloration evolved, there arose a selective advantage for tasty animals to resemble poisonous ones.
mountain king snake
-harmless-
coral snake
DEADLY

8. Anglerfish closely resemble algae-covered rocks, dangling a small
Aggressive Mimicry
Predators try to resemble harmless animals.
Like a “wolf-in-sheep’s-clothing.”
Anglerfish closely resemble
algae-covered rocks, dangling a small
lure from their upper lip awaiting a
victim.

9. Coevolution of Plants and Herbivores
Plants have evolved many adaptations that deter prey.
FACT: milkweed synthesize toxic and distasteful chemicals
RESULT:
animals learn rapidly not to foods that make them sick
animals immune to the toxin have plenty to eat
certain insects evolved to utilize the toxin (stored in their own tissues as a defense against their own predators)
certain insects evolved to detoxify the chemical

10. Coevolution of Plants and Herbivores II
FACT: Grasses have evolved a tough silicon substance in the blade (leaf) that deters predators except those with strong, grinding teeth and powerful jaws.
RESULT: zebra (Equus) have evolved longer teeth w/ thicker enamel coatings that resist wear
FACT: very tall Acacia trees (African savanna) have evolved thorns to deter predators.
RESULT: giraffes have evolved longer necks and agile tongues that enable them to munch on the leaves undeterred by their height and long thorns.

11. Symbiotic Relationships - PARASITISM
parasites (generally) are much smaller than their prey
often live in (endoparasites)or on (ectoparasites) their host without killing them
ie. tapeworms, fleas, bacteria, viruses, protozoa
bore into their victims and suck out blood and other body tissues

12. Competition
Competition – the use of the same limited resource by two or more species in the same place at the same time
Resource = anything necessity of life (water, nutrients, light, food, or space)
Competition may cause the development of different niches or physical characteristics.

13. Competition
Organisms may develop physical differences because of competition for resources.
Character Displacement – evolution of anatomical differences that reduces competition
Happens most where ranges of competitors overlap
ie. Darwin’s finches
Species found in separate locations have the same beak size
The same species found together have different beak sizes allows them to feed on different seeds and reduces competition

14. Resource partitioning...
Though the niches of closely related species often overlap considerably, each species develops a number of distinctive behaviors that allows them to exploit slightly different parts of their shared environments.
ie. horned puffins dig out nests near the top of the cliffs...tufted puffins utilize existing crevices, slightly lower in the cliffs
Furthermore, each species employs slightly different hunting tactics, nest at slightly different times, and adopts other characteristic quirks that serve to reduce head to head competition between the two species.

15. Symbiotic Relationships - MUTUALISM
two organisms interact in a way that benefits both
numerous in the living world & have a significant impact on nearly all the Earth’s ecosystems
ie. spreading of pollen by birds, insects, & animals – animal obtains energy (nectar, fruit) & plant gets pollinated

16. MUTUALISM - continued
trees are critically dependent on mutualistic relationship with fungi that provide them with essential nutrients from the soil
herbivores dependent on intestinal bacteria

17. Symbiotic Relationships - COMMENSALISM
relationship between two species benefits one without affecting the other
ie. birds & herbivores
ie. birds & (nesting) trees
ie. orchids & tropical trees
barnacles & marine mammals

18. Name the Symbiotic Relationship…
A eagle hunting a mouse.
Predation
A tick feeds on the blood of its host and may carry disease
Parasitism
The flower lives on a tree and absorbs the water from runoff and the tree is unaffected.
Commensalism
Two different types of finches feeding on seeds.
Competition
An ant protects a caterpillar from predators and the caterpillar produces a sweet liquid for it to drink.
Mutualism