ECO TEST 6: Ch 19&20

Community Structure and Succession

distinct or gradual

Communities can have ____ boundaries 

Zonation of Terrestrial Communities

Boundaries caused by different abiotic conditions, competitions among species. Results in distinct zones of communities named for dominant or common species.

Ecotone

A boundary created by sharp changes in environmental conditions over a relatively short distance, accompanied by a major change in the composition of species

“the ecotone fallacy”

Many species are adapted to each of the habitats, but can also persist in the ecotone. Ecotones often support a high number of species: ____

Serpentine Soils

Derived from weathering rocks with high levels of nickel, chromium and other heavy metal.

several serpentine adapted species

Serpentine soils are toxic to many plant species, but home to 

sharp ecotone

There is ____ between serpentine barrens and adjacent forest community

Interdependent communities

Communities in which species depend on each other to exist

• Species interaction (mutualism, predator-prey, etc.) are ubiquitous

• Species composition of communities should be predictable based on interactions

• Communities resemble superorganisms

Independent communities

Communities in which species do not depend on each other to exist

• Species presence/absence based on abiotic tolerances of each species

• Species composition may be unpredictable

• Can predict the pool of potential species, but not actual community

Independent species distribution

Line transect along a moisture gradient in the Great Smoky Mountains. Each species reaches peak abundance at a different point. This shows ____ between one another.

reduced competition

Neighbor removal experiment at high vs. low elevation sites.

• At low elevation, removing neighbors increased survival and flowering (____)

neighboring plants facilitate, interdependence of species

Neighbor removal experiment at high vs. low elevation sites.

• At high elevation, removing neighboring plants reduced survival and flowering (____, ____)

number and relative abundance

Community diversity incorporates both the ____ of species.

Species richness

The number of different species in a community

Absolute abundance

The number of individuals of an individual species in a community

Relative abundance

The proportion of individuals in a community represented by each species

Species evenness

A comparison of the relative abundance of each species in a community

Log-normal distribution

Species frequently exhibit a ____ of abundance. Few very common & very rare species. Most species have intermediate abundance.

log scale

Normal distribution when plotted on a ____

Rank-abundance curve

Plots the relative abundance of each species in a community in rank order from the most abundant species to the least abundant species

richness; evenness

Rank-abundance curves illustrate species richness and species evenness. Both communities have equal species richness. Community B has higher species evenness than Community A

• Length along x-axis: ____

• Slope of the line: ____

higher; slightly higher

Lizard communities in primary forests vs plantations in Brazil. Primary forest support ____ species richness, but ____ evenness in plantations

resources, habitat diversity, keystone species; disturbance

Species diversity is affected by____, ____, ____,  and ____

intermediate productivity

Hump-shaped distribution is the most common: highest diversity a

Low productivity

Only very tolerant species can persist (Effects of productivity and species richness)

High Productivty

Most competitive species outcompete other species (Effects of productivity and species richness)

places to feed and breed

Communities with a higher diversity of habitats should offer more potential niches (e.g., ____) and a higher diversity of species

bird species

Forests with more diverse foliage heights had greater diversity of ____.

Keystone species

A species that substantially affects the structure of communities despite the fact that individuals of the species might not be particularly numerous

keystone predator

Sea stars are a ____ in the intertidal zone. Predation keeps mussel species below K, limits interspecific competition.

Ecosystem engineer

A type of keystone species that substantially affects communities by changing the structure of the landscape

community plants and animals present

Beavers convert flowing streams into standing ponds, changing the ____

Intermediate disturbance hypothesis

The hypothesis stating that more species are present in a community that occasionally experiences disturbances than in a community experiencing frequent or rare disturbances

herbivory

Density of snails manipulated to vary intensity of disturbance through ____. A

intermediate levels of disturbance

Algal species richness was highest at ____

food webs

Communities are organized into 

Food web

A representation of how different species in a community feed on each other

direction of energy

Arrows indicate the ____ movement through the food web.

regulate the abundance

Predation and herbivory are key aspects that ____ of different species in communities

Direct effect

An interaction between two species that does not involve other species

• Fish prey on larval dragonflies (-)

• Dragonflies feed on bees (-)

• Bees pollinate flowers (+)

Indirect effect

An interaction between two species that involves one or more intermediate species

indirectly

Fish reduce the population of dragonflies allowing higher population of pollinators. Fish ____ increase the pollination rate of flowers.

no direct effect

Low concentrations of the pesticide Malathion do not harm leopard frog tadpoles meaning there is ____

indirect

Other ____effects through the effects of Malathion on other species in the community include

• Malathion reduced zooplankton (-)

• Algal bloom of phytoplankton (+)

• Shaded out Periphyton (-)

• Decreased food for Leopard (-)

Density-mediated indirect effect

An indirect effect caused by changed in the density of an intermediate species

density

Sea stars reduce the ____ of mussels in the intertidal zone. This allows other species like snails to occupy limiting space on the rock

Trait-mediated indirect effect

An indirect effect caused by changes in the traits of an intermediate species

reintroduction of wolves

Trait-mediated indirect effects can be seen through the ____ into Yellowstone National Park

• Change in behavior elk

• Less browsing in some areas

• rebound in tree population

• increase in songbird diversity

Trophic cascade

Indirect effects in a community where effects from one trophic level have effects at multiple trophic levels above or below

Bottom-up cascade

When the abundances within trophic groups are determined by the amount of energy available from the producers in a community

Top-down cascade

When the abundance within trophic groups is determined by the activity of predators at the top of the food web

replace each other over time

Succession occurs in a community when species ____

plant communities

This example of a direct observation of succession shows a diversity of ____

• 1794: Captain George Vancouver finds 32km wide glacier blocking bay

• 1879: John Muir finds open water

Chronosequence

A sequence of communities that exist over time at a given location

Chronosequence

Sediment cores from lakes:

• Yearly accumulation

• can identify pollen from specific species to identify past communities

This is an example of ____?

Primary succession

The development of communities in habitats that are initially devoid of plants and organic soil, such as sand dunes, lava flows, and bare rock

mossess, lichens, drought-tolerant grasses

Examples of primary succession include ____. Accumulation of organic material allows further succession

Secondary succession

The development of communities in habitats that have been distributed and include no plants but still contain organic soil

abandoned for various length of times

An example of secondary succession includes former agricultural fields. Duke forest contains farms that were ____

animal communitiesSucce

Succession is usually described in terms of changes in plant communities. However, changes in plants are typically mirrored by changes in ____

mechanisms

Succession can occur through different ____

Facilitation

A mechanism of succession in which the presence of one species increases the probability that a second species can become stablished

colonize

Early successional species can change the environment in ways that make it easier for later successional species to ____

nitrogen-fixing bacteria

Earlier successional plants add organic material to the soil, provide shade etc. One specific example Alder trees host ____ in their roots

Inhibtion

A mechanism of succession in which one species decreases the probability that a second species will become established

further change

Intense competition in climax communities prevents ____ in community structure

Prior effect

When the arrival of one species at a site affects the subsequent colonization of other species

colonization

Ex. of Priority effect: When Bryozoans colonize ocean rocks, they can prevent further ____ by sponges, tunicates, etc.

Tolerance

A mechanism of succession in which the probability that a species can become established depends on its dispersal ability and its ability to persist under the physical conditions of the environments

low nutrients, and intense sunlight

Early successional plant species are tolerant of ____

shade and competition

Late successional plant species are tolerant of ____

tolerance; inhibition

Scrape intertidal zone rocks clean and document pattern of succession

• Little brown barnacles initially colonize (____)

• Eventually outcompeted by acorn barnacles (____)

facilitate

(Test of succession results) 

• removing little brown barnacles had little effect

• removing acorn barnacles resulted in much less algal growth

• providing acorn barnacle shells increased algal growth

Acorn barnacles ____ the growth of algae by providing structure for algae to grow

permanent single climax

Succession does not always produce a ____ community

frequency + density + basal area

Old growth forest in PA. Understory (younger) tree community predicts what the canopy will look like in the future. Oak, Hickory, tulip poplar being replaced by species tolerant of shade and deer browsing like beech.

Importance value: ____

Transient climax community

A climax community that is not persistent

permanent establishment

Frequent disturbance may prevent ____ of a climax community

Vernal ponds dry up for part of the year. Succession restarts each spring when water returns