BIOS 120 Summer 2026 Exam 2

UIC

community

assemblage of plant, animal, fungal, and microbe populations that live in a particular area of habitat

inteaction

characterizes communities

explains the underlying mechanisms that create, maintain, and determine the fate of biological communities

community ecology

patterns

vegetation zonation, species lists, seasonal distribution of activity, and association of certain species

processes

herbivory, competition, predation risk, nutrient availability, patterns of distribution, energy flow, history, and evolution

emergent properties of community

• spatial and temporal structure

• species richness

• species diversity (even-ness)

• trophic structure

• succession and disturbance

spatial structure

way species are distributed relative to each other

examples of spatial structure

• trees in rainforest that are stratified into different levels

• epiphytes on trees

temporal structure

timing of appearance and activity of species

species richness

number of species in a community

diversity

number of species in the community and their relative abundances

ecological succession

more or less regular colonization, recovery, and turnover (replacement) of species within a community following a disturbance

examples of ecological succession

• bog community —> black spruce forest

• forest fire destroying large area of trees —> meadow —> back into the forest

• lava —> vegetation —> forest

disturbance

events such as floods, fires, droughts, overgrazing, and human activity that alter communities by eliminating species, reducing population sizes, and altering resource availability, climate, and physical properties

primary succession

disturbance results in a sterile, novel environment. Succession can only proceed through the colonization of species from elsewhere. involves major temporal dynamics in the physical (starts with bare rock)

secondary succession

disturbance may extirpate some species but others survive at low population sizes. involves both recovery and colonization of species. less dramatic temporal dynamics in the physical environment (already have something intact, just beat it back, don’t annihilate it)

lichens

grow on lava, starts the process of primary succession

agents of disturbance for primary succession

• volcanoes

• asteroids

• retreating glaciers

• sand dune formation

• completely paved by development

agents of disturbance for secondary succession

• fire

• huricanes & tornadoes

• floods

• abandoned farmland or other human landscapes (detroit)

• clear-cuts in forests

early successional

high intrinsic growth rates, good dispersal and establishers, tolerate physical and climatic stress, poor competitors and/or susceptible to herbivores or predators

late successional

high carrying capacties, often poorer dispersers, less tolerant of physical stress, strong competitors and predators

faciliation

early successional species modify the environment, and create opportunities for subsequent species to invade or establish. tend to speed succession and make succession regular and predictable

inhibition

early species, via priority effects, gain an advantage and slow the establishment of later species, slowing succession and making it less predictable (exception to ecological succession)

disturbance characteristics that succession endpoint depends on

• amplitude and frequency

• climax communities more likely when disturbances are high amplitude and low frequency

• disturbance communities are those with high frequency of low amplitude disturbances

• intermediate amplitudes and frequencies may maximize species richness and diversity

climax community

more/less permanent and final stage of a particular succession, often characteristic of a restricted area, characteriezed by slow rates of change, dominated by species tolerant of competition for resources

trophic interaction

transfer of energy (eating, decomposing, obtaining energy via photosynthesis)

trophic structure

hierarchy of feeding in a community

food web

diagram of trophic interactions (energy flows from bottom to top)

Who is a primary consumer

zooplankton

Who is a secondary consumer

mackerel

What is phytoplankton

primary producer

What is harbor seals?

tertiary consumer

What is killer whales

quantiary consumer

Elton niche

Where does it live? What does it eat? Who eats it?

Hutchinson niche

fundamental niche describes the range of climatic and physical conditions that can support the species in the absence of negative biotic interaction

realized niche

the actual range of conditions that a species can succeed including competition and predation from other species

species often create ___ for other species

niches

keystone species

disproportionately important in communities, act to maintain species diversity, extinction = niches eliminated for many other species, modifies the environment in such a way that other organisms are able to live, or is a predator that maintains diversity at a certain trophic level

examples of keystone species

• California Sea Otters: This species preys upon sea urchins, allowing kelp forests to become established.

• Pisaster Starfish: Grazing by Pisaster prevents the establishment of dense mussel beds, allowing other species to colonize rocks on the Pacific Coast.

• “Mangrove” Trees: Mangrove seeds disperse in salt water. They take root and form a dense forest in saltwater shallows, allowing other species to thrive

• The Acorn Banksia: At certain times of year, Banksia prionotes is the sole source of food for honeyeaters, which in turn are the pollinators for many other species of plants in Western Australia.

competition

occurs when individuals of the same or different species restrict each others’ access to limiting resources, may be prey, water, light, nutrients, nest sites, etc.

intraspecfic competition

competition among members of the same species

interspecific competition

competition among individuals of different species

exploitation competition

occurs when individuals permanently or temporarily use up the limiting resource or resources, thus depleting the amount available to others

interference competition

occurs when individuals via antagonistic behaviors or caching behaviors prevent others from accessing the limiting resource (territoriality, dominance hierarchies)

examples of interference competition

flour beetle and red flour beetle canibalize the eggs of their own species, as well as each others, interfering with the survival of potential competitors

can cause exclusion of one species

exploitation competition

How can exploitation create coexisting?

species can coexist with a decrease in their potential for growth by partitioning the resources

A.J. Lotka and V. Volterra

developed model of population growth to predict outcome of competition

competitive exclusion principle

Two species cannot compete for the same limiting resource for long. Even a minute reproductive advantage leads to the replacement of one species by the other

What did G.F Gausse’s experiment demostrate?

Paramecium aurellia outcompetes and displaces Paramecium caudatum in mixed laboratory cultures, apparently confirming the competitive exclusion principle.

resource partitioning

Species that share the same habitat and have similar needs frequently use resources in somewhat different ways - so that they do not come into direct competition for at least part of the limiting resource; evolutionary response to interspecific competition

best known example of resource partioning

• As many as five different species of anoles may exist in the same forest, but each stays restricted to a particular space: some occupy tree canopies, some occupy trunks, some forage close to the ground. 

• When the brown anole was introduced to Florida from Cuba, it excluded the green anole from the trunks of trees and areas near the ground: the green anole is now restricted to the canopies of trees:the resource (space, insects) has been partitioned among the two species 

Gausse’s rule

two organisms cannot occupy exactly the same niche

Joseph Connel’s Barnacle experiment

• In the early 1960s, ecologist Joseph Connell studied how interspecific competition determines the stratified distribution of two barnacle species on the Scottish coast: Semibalanus balanoides (lower shore) and Chthamalus stellatus (upper shore).

• His objective was to determine the extent to which competition imposed this relationship between the two

• When Chthamalus was removed from the upper zone, Semibalanus could not replace it due to an inability to survive desiccation at low tides. Its realized niche matches its fundamental niche

• When Semibalanus was removed from the lower zone, Chthamalus successfully moved in, revealing it is normally excluded by a stronger competitor. Its realized niche is smaller than its fundamental niche.

commensalism

interspecific interaction where one species benefits and the other is unaffected

examples of commensalism

• ant colonies have rove beetles as commensals, beetles mimic ants behavior and pass as ants, eat detritus and dead ants

• anemonefish live within anemones tentacules, have specialized mucus membranes that render them immune to anemone’s stings, gain protection by living like this

• birds nesting in trees

inquilines

Commensal organisms that frequently live in the nests, or on the bodies, of the other species

mutualism

interspecific interaction between two species that benefits both members; Populations of each species grow, survive, and/or reproduce at a higher rate in the presence of the other species.

examples of mutualism

• rooting plants have mutualistic associations with fungal mychorrhizae. Mychorrhizae increase the capability of plant roots to absorb nutrients. In return, the host provides support and a supply of carbohydrates.

• Many corals have endosymbiotic organisms called zooxanthellae . These mutualists provide the corals with carbohydrates via photosynthesis. In return, they receive a relatively protected habitat from the body of the coral

• Flowering plants and pollinators. (both facultative and obligate) 

• Parasitoid wasps and polydna viruses. (obligate) 

• Ants and aphids. (facultative) 

• Termites and endosymbiotic protozoa. (obligate) 

• Humans and domestic animals. (mostly facultative, some obligate)

mutualistic symbiosis

type of mutualism in which individuals interact physically, or even live within the body of the other mutualist; essential for survival of at least one member

example of mutualistic symbiosis

lichen is fungal-algal symbiosis, fungal hyphae provides a protected habitat for the algae and takes up water and nutrients for the algae, in return, the algae provide carbs as source of energy for fungus

facultative mutualisms

not essential for the survival of either species. Individuals of each species engage in mutualism when the other species is present. 

obligate mutualisms

essential for the survival of one or both species

Predators, parasites, parasitoids, and herbivores

obtain food at the expense of their hosts or prey. 

parasties and pathogens

smaller than their host

evidence that parasites may have one or many hosts during their lifetime.

• Some even steal parental care or other resources 

• Parasites consume their host either from the inside (endoparasites) or from the outside (ectoparasites). 

• Pathogens are parasitic disease-causing microbes.

Parasitoids

hunt their prey like predators, but lay their eggs within the body of a host, where they develop like

introduced species

species that has been intentionally or unintentionally introduced by humans. Exotic species are species that are not native to an area (often used synonymously with introduced, but exotics sometimes arrive on their own).

naturalized species

species that has spread beyond its point of introduction and become established

invasive species

causes ecological harm to communities, usually by changing the community in ways that cause the extinction of other species, or alternately, cause damage to human economic well being

How are earthworms invasive species?

• earthworms and others were introduced to many parts of the world by European settlers in the 1600s and 1700s.

• They alter forest communities by breaking up a thick layer of detritus that naturally occurs on the floor (exactly what they are valued for in gardens and farms), creating drier soil with fewer leaf litter organisms.

ecosystem

unit composed of all the living things in a single place at a given time, in addition to, the important non-living components of the system; encompasses all aspects of a biological community, in addition to factors such as rates of CO₂ uptake, rates of nitrogen fixation from the atmosphere, precipitation, seasonal flooding and its effects on nutrients, etc.

nonliving components of an ecosystem

sunlight, rainfall, silica and clay particles in the soil, the air, the water in the soil,

biosphere

largest and most encompassing ecosytem we know; encompasses all the plants and animals on Earth

ecosystems ecology

concerns itself with the flow of energy and biomass

common to all biological communties

nutrient cycling and energy flow

sun

ultimate energy source for almost every ecosystem on Earth

hydrothermal vent communties

don’t rely on sun for energy, rely on geothermal energy, but still depend upon oxygen fixed by photosynthetic organisms

How does energy enter ecosystems

via photosynthesis or for a few exotic ecosystems chemosynthesis

producers

bring energy into an ecosystem; include green plants, algae, cyanobacteria, etc..anything that can capture energy from nonliving components of the environment.

All metabolic processes consume ___ in some way, and in each reaction, much of it is effectively “wasted

energy

How does biological energy radiate into the environemnt

as infrared light

what happens to energy as it passes through trophic levels

its lost

energy is

transferred, not recycled (must be continually replenished from the sun)

What’s the difference between matter and energy

energy does not recycle, matter recycles through ecosystems

How does matter recycle?

Atoms of every biologically important element constantly recycle through ecosystems, into the abiotic component of the biosphere, and back into living systems.

decomposition

through this process, each element ultimately becomes nonliving, and has the potential to re-enter the biosphere again.

example of matter recycling

in a freshwater pond, green plants and photosynthetic algae fix atmospheric CO₂ using sunlight as an energy source, creating biological molecules that serve as carbon skeletons and energy carriers.

• They also retrieve other elements, such as iron and calcium, from their environment, and pass them up the food chain as well.

What happens to the biomass created by producers

a significant fraction is eaten by herbivores and passed up the food chain; the rest is stored in temporary biological reservoirs in the tissues of plants, but ultimately decomposes when the plant dies

How is energy liberated/released back into the environment

by living things that consume the living or dead plants, leaves the Earth as heat

matter

cycles between living and non-living things, no new matter leaves/reaches Earth

food web

schematic diagram that describes the trophic interactions in a community; also documents patterns of energy flow

food chain

one path through a food web, from bottom to top; limited number of links

decomposition

trophic interaction that uses up the energy left over in dead bodies of organisms, sometimes depicted in food webs

biomass

weight of living matter; usually measured in dry weight per unit area

pyramid of biomass

figure that quantifies the relative amounts of living biomass found in each trophic level; in most environemnts the amount of biomass decreases as one moves from bottom to top of food chain

wood

oldest fuel that can be burned and converts biomass into CO2, H2O and energy

productivity

rate at which biomass accumulates

primary consumers

eat producers, generally posses significantly less biomass than producers

secondary consumers

consume primary consumers