Community Ecology Flashcards
What is a biological community?
A group of populations of different species living close enough to interact
What are interspecific interactions?
Interactions with individuals of other species in the community- competition, predation, herbivory, symbiosis, and facilitation
What is interspecific competition, and what kind of interaction is it?
a -/- interaction that occurs when individuals of different species compete for a resource that limits their growth and survival
What is competitive exclusion?
A local elimination of the inferior competitor due to two species competing for the same limiting resources and that they cannot coexist permanently in the same place
What is ecological niche?
The sum of a species’ use of the biotic and abiotic resources in its environment
What does it mean to say that two species cannot coexist permanently in a community if their niches are identical?
The will eventually kill the other species off because they are competing for the same food source BUT ecologically similar species can coexist in a community if one or more significant differences in their niches arise through time
What is resource partitioning?
The differentiation of niches that enables similar species to coexist in a community
What is fundamental niche?
The niche potentially occupied by that species
What is realized niche?
The portion of its fundamental niche that it already occupies
Tell me about the experiment with barnacles shown in the next slides. What do you think would happen if Chthamalus rather than Balanus was removed? Why?
The Balanus would begin to grow where the Chthalamus was previously
What’s the deal with the common spiny mouse and the golden spiny mouse?
Golden spiny mouse had become diurnal (active during the day) even though they are naturally nocturnal; did this in order to overcome competition with the nocturnal common spiny mouse
What is character displacement?
Tendency for characteristics to diverge more in sympatric (geographically overlapping) than in allopatric (geographically separate) populations of two species
What’s the deal with the finches shown in the next slide?
Allopatric populations of two finch species have similar beak morphologies and presumably eat similarly sized seeds; however when the two species are sympatric they developed different size beaks
What is predation, and what kind of interaction is it?
+/- interaction between species in which one species, the predator, kills and eats the other, the prey
Predators have adaptations for capturing prey. What sorts of adaptations do predators have?
Acute senses that enable them to find and identify prey, claws, fangs, poison, fast, agile
Prey animals have adaptations for avoiding predators. What are they?
Hiding, fleeing, forming herds, alarm calls, mechanical and chemical defense, toxins, warning coloration, camouflage (cryptic coloration)
Many predators also use mimicry. How the mimic octopus uses mimicry?
Takes the appearance and movement of more than a dozen marine animals including crabs, sea stars, snakes, fish, stingrays
What is herbivory, and what kind of interaction is it?
+/- interaction in which an organism eats parts of a plant or alga
Herbivores have many specialized adaptations. What sorts of adaptations do they have?
Chemical sensors on their feet to distinguish between plants (insects), sense of smell to examine plants, specialized teeth or digestive systems adapted for vegetation
Plants have adaptations for protection against herbivores. What sorts of adaptations do they have?
Chemical toxins or structures such as spines and thorns
What is symbiosis in the broad sense?
When individuals of two or more species live in direct and intimate contact with one another
What is parasitism and what kind of interaction is it? What is an endoparasite? What is an ectoparasite?
+/- symbiotic interaction in which on organism, the parasite, derives it nourishment from another organism, its host, which is harmed in the process
What is mutualism and what kind of interaction is it? What is obligate mutualism? What is facultative mutualism?
+/+ interspecific interaction that benefits both species;
one species has lost the ability to survive on its own;
both species can survive alone
What is commensalism and what kind of interaction is it?
+/0 interaction between species that benefits one of the species but neither harms nor helps the other
What is facilitation and what kind of interaction is it?
+/+ or +/0 Species can have positive effects on the survival and reproduction of other species without necessarily living in the direct and intimate contact of a symbiosis
What is species diversity?
The variety of different kinds of organisms that make up the community
What is species richness?
The number of different species in the community
What is relative abundance?
The proportion each species represents of all individuals in the community
Which community do you think is more diverse?
Community 1: 25A, 25B, 25C, 25D
Community 2: 80A, 5B, 5C, 10D
Community 1
What do we mean by trophic structure of a community?
The structure and dynamics of a community also depend on the feeding relationships between organisms
What is a food chain?
Primary producers– primary consumers–secondary consumers–tertiary consumers–quaternary consumers
What is a food web?
Food chains linked together to show trophic relationships in a community using arrows that link species according to who eats whom
Why are food chains and food webs relatively short?
Energy expenditure
What is the energetic hypothesis?
Suggests that the length of a food chain is limited by the inefficiency of energy transfer along the chain (only around 10% is passed on)
What was this experiment and what did it show about the energetic hypothesis?
researchers manipulated the productivity of tree-hole communities in Australia, by providing leaf litter input at three levels, Reducing energy input reduced food chain length, a result consistent with the energetic hypothesis
What are dominant species?
The species that are the most abundancy or that collectively have the highest biomsss
What’s the American chestnut story?
American chestnut was a dominant tree in easter North America before 1910 making up 40% of mature trees– humans accidentally introduced the fungal diseases chestnut blight to NYC from Asia; this killed off almost all chestnut trees; other trees began to replace chestnuts; mammals and birds weren’t affected but moths and butterflies that fed on the tree became extinct
What are keystone species?
Not usually abundant in a community; exert strong control on community structure but not by numerical might but by their pivotal ecological niches (roles)
What’s the sea star story?
they feed on mussels; shows that piaster acts as a keystone species, exerting an influence on the community that is not reflected in its abundance
What are ecosystem engineers (foundation species)?
Species that dramatically alter their environment
What’s the beaver story?
Felling trees, building dams, creating ponds, beavers are able to transform large areas of forest into flooded wetlands making them ecosystem engineers
Let’s consider the possible relationships between plants (V for vegetation) and herbivores (H).
What does V –> H mean?
What does V
that an increase in vegetation will increase the numbers or biomass of herbivore but not vice versa;
an increase in herbivore biomass will decrease the abundance of vegetation, but not vice versa
V –> H suggests a bottom-up model. What’s that?
postulates a unidirectional influence from lower to higher trophic levels
If N stands for mineral nutrients and P stands for predator number, what does the following mean?
N –> V –> H –> P
the presence or absence of mineral nutrients (N) controls plant (V) numbers, which controls herbivore (H) numbers, which in turn control predator (P) numbers
N –> V –> H –> P
If this really is a one-way system, what would altering N do? What would altering P do? If you alter N, what happens at each level?
altering N affect P but alter P does not effect any level
What a top-down model
predation mainly controls community organization because predators limit herbivores, herbivores limit plants, and they limit nutrient levels through nutrient uptake
The top-down model can have practical applications. What is biomanipulation?
approach of using the top-down model to improve water quality in polluted lakes
What is the nonequilibrium model?
Most communities are constantly changing after disturbance
What do we mean by disturbance?
An event, such as a storm, fire, flood, drought or human activity, that changes a community by removing organisms from it or altering resource availability
What is the intermediate disturbance hypothesis?
Moderate levels of disturbance foster greater species diversity than do high or low levels of disturbance
Why would high levels of disturbance reduce community diversity?
Create environmental stresses that exceed the tolerances of many species or by disturbing the community so often that slow growing or slow colonizing species are excluded
Why would low levels of disturbance reduce community diversity?
Can reduce species diversity by allowing competitively dominant species to exclude less competitive ones
What is ecological succession?
The disturbed area may be colonized by a variety of species, which are gradually replaced by other species, which are in turn replaced by still other species
What is primary succession?
When the process begins in a virtually lifeless areas where soil has not yet formed
What is secondary succession?
Occurs when an existing community has been cleared by some disturbance that leaves the soil intact
What are facilitation and inhibition in the context of succession?
Early arrivals may facilitate the appearance of the later species by making the environment for favorable
Early species may inhibit establishment of early later species
What is the pioneer stage?
The exposed glacial moraine is colonized first by pioneering species that include liveworts, mosses, firewood, scattered Dryas, and willows
What is the Dryas stage?
After about three decades, Dryas dominates the plant community
What is the spruce stage?
In the next two centuries, these alder stands are overgrown first by Sitka spruce and later by wester hemlock and mountain hemlock
What is the alder stage?
A few decades later, the ares is invaded by alder, which forms dense thickets up to 9 m tall
How is succession on glacial moraines related to environmental changes caused by transitions in the vegetation? How about changes in pH of the soil?
How about changes in soil concentrations of mineral nutrients? How about nitrogen?
Bare soil after glacial retreat is low in nitrogen content, so pioneer plant species begin succession with poor growth and yellow leaves
Soil nitrogen content increases quickly during alder stage and keeps increasing by spruce stage
How is human-caused disturbance affecting communities? What are some examples of human-caused disturbance?
Agricultural development, rain forests are disappearing due to cutting of lumbar, cattle grazing, farmland; boats dragging nets on the bottom of ocean floor scrape corals and other life
Because disturbance by humans is often severe, what usually happens to species diversity?
Reduces species diversity in many communities
