1. INTERSPECIFIC INTERACTIONS
Predation: The predator eats the prey.
Parasitism: The parasite derives its nourishment from the host, which is harmed in the process.
-This is a (+-) interaction because one species benefits, while the other does not.
-Also includes herbivory, the herbivore eating a plant
-Predators usually have acute senses to locate prey, and adaptations, such as fangs, claws, stingers, and poison, to assist in capture
-Example: Rattlesnakes and vipers locate prey with heat-sensing organs, and kill with injection of toxins through their fangs , or a lion finding its dinner as shown in the link
Defenses
-plants employ the use of chemicals that make them distasteful or harmful to the predator, which learns through trial and error which plants to avoid
-animals have a variety of protection, which includes:
-cryptic coloration: any color, pattern, shape or behavior that enables an animal to blend in with the surrounding
-aposematic coloration: conspicuous patterns or colorations that warn predators that they sting, bite, taste bad, and need to be avoided
-Müllerian mimicry: Occurs when several animals, all with some special defense mechanism, share the same coloration. An effective strategy because a shared pattern is more easily learned by a predator, versus different patterns for every animal (ie yellow and black of bees, wasps, yellow jackets)
-Batesian mimicry: Occurs when an animal without any special defense mimics the coloration or actions of animals that do such as an owl that makes the sound of a hissing rattlesnake
Commensalism: a relationship between a host and its symbiont where one partner benefits without significantly affecting the other.
-Example: barnacles that attach to whales
-Because only one species is being affected by commensalism, any evolutionary change in the relationship is likely to occur in the species that is benefiting.
Mutualism: a relationship between a host and its symbiont where both partners benefit from the relationship. It requires the evolution of adaptations in both participating species, because changes in either species are likely to affect the survival and reproduction of the other.
-Example: the protozoa that digests cellulose in the gut of termites
-Many mutualistic relationships may have evolved from predator-prey or host-parasite interactions.
Competition: results when two or more species are after the same kinds of resources
-expands to include competition for food, habitats, or any other resource that is limited
-Example: a species of squirrels called Sciurus carolinensis or grey squirrels have over taken another species of squirrels in Canada called the Sciurus vulgaris or red squirrels. A competiton for food ensued and soon, the original inhabitants of the land, the red squirrels, started to decrease in population
-entails competitve exclusion principle outlined below
2. THE COMPETITIVE EXCLUSION PRINCIPLE (G.F. Gause's principle)
DEFINITION: This is when two species compete for exactly the same resources or occupy the same niche. Only one will turn out to be more successful because one species outcompetes the other and the second species is eliminated. No two species can sustain coexistence if they occupy the same niche.
HOW IT AFFECTS COMMUNITY STRUCTURE: A small advantage for one species can lead to elimination of the inferior competitor (extinction), and there will be an increase in density of the superior one.
EXPERIMENT: Gause mixed two types of Paramecium that competed for the same food. One population used the resources more efficiently and eventually grew more, eliminating the 2nd species.
3. FUNDAMENTAL NICHE vs. REALIZED NICHE
Ecological niches are the sum total of an organism's role in an environment using the biotic and abiotic resources available in their habitat or ecosystem.
-Example: a plant's niche or job in a park is to photosynthesize to convert carbon dioxide in the atmosphere into oxygen gas which can be utilized by animals. The animals, in turn, function so in their niche by consume the oxygen gas and producing the carbon dioxide that the plant thrives off of. Many cases of mutualism arise from these established niches. As Eugene Odum put it, if an organism's habitat is its address, its ecological niche is its occupation. There are two distinct niches that arise in an ecosystem:
-A fundamental niche is the set of resources an organism is theorized to be capable of using under ideal circumstances. In other words, the fundamental niche are resources that an organism is believed to be able to utilize.
-However, in reality there are circumstances that do often times sacrifice the ideal circumstances that organisms thrive under. These cases may include instances of predation or competition for resources. This leaves a population with the resources it actually does use collectively. This is called the realized niche.
4. RESOURCE PARTITIONING
The division of environmental resources by coexisting species populations such that the niche of each species differs by one or more significant factors from the niches of coexisting species populations.
-interaction between Sympatric species, which consume slightly different foods or use other resources in slightly different ways
-Sympatric species show differences in morphology and resources they use
-Example: Seven species of Anolis lizards live closely together in the same habitat. Each species exists in a characteristic microhabitat, distinguished by the amount of sunlight received and the size of vegetation.
Character Displacement: The tendency for more pronounced divergence in morphology in sympatric populations of two species than in allopatric populations of the same two species.
-Example: Galapagos Islands finches
5. PRIMARY & ECONDARY SUCCESSION
Ecological succession: transitions in species composition over ecological time
Primary Succession
-begins in an essentially lifeless area where soil has not yet formed like a new volcanic island, rubble left behind by a retreating glacier
-Example: Glacier Bay, Alaska
-is first occupied by mosses and lichens, then by dwarf willows
-after 50 yrs alders form dense strands
-eventually give way to Sitka spruce, later joined by hemlock, forming relatively stable spruce-hemlock forest (we recognize as taiga)
-entire process app. 200 years
Secondary Succession
-occurs where an existing community has been cleared by some disturbance that leaves the soil intact
-begins a return to something like its original state
-Example: old-field succession in Piedmont region of North Carolina
-agricultural fields abandoned
-an herbaceous community composed mostly of annual crabgrass develops during 1st yr
-followed by other herbaceous plants
-by 3rd yr, pine seedlings invade field
-replaced by climax community (relatively stable state after a sequence of predictable transitional stages) dominated by oaks and hickories, the vegetation that originally occupied the site before farmers cleared it for planting
