Chapter 58 Community Ecology

As these plants die, they add more___________ to the soil and soon a few _____ will appear. The shrubs are then followed by _____.

decayed organic matter; shrubs; trees

The ____________ of the carcass has enriched the surrounding sediments, attracting:

decomposition; a new population of sediment dwellers such as marine worms.

individualistic model

described a community as an assemblage of species coexisting primarily because of similarities in their physiological requirements and tolerances. Although acknowledging that some assemblages of species were fairly uniform and stable over a given region, Gleason suggested that distinctly structured ecological communities usually do not exist. Instead, communities are loose assemblages of species distributed independently along an environmental gradient. communities do not necessarily have sharp boundaries, and associations of species are much less predictable and integrated

Succession can take place even in marine environments when a __________ occurs.

disturbance

Sere

each phase of succession.

Pioneer Species appear

early in succession

Tolerance

early successional species are characterized by r-selected species tolerant of harsh conditions. any species can start the succession, but the eventual climax community is reached in a somewhat orderly fashion The species that establish and remain do not change the environment in ways that either facilitate or inhibit subse- quent colonists.

Facilitation

early successional species introduce local changes in the habitat. K-selected species replace r-selected species ach colonizing species makes the environment a little different—a little shadier or a little richer in soil nitrogen—so that it becomes more suitable for other species, which then invade and outcompete the earlier residents.

to measure species diversity:

ecologists need to take into account number of species in a community and relative abundance. need to calculate diversity index

As a general rule, the closer a community is to the _______, the ____________ it will contain.

equator, more species

The combination of ________ from rocks, and the __________________ from the lichens will begin to form a thin layer of ____ in which a few__________ organisms can grow.

minerals; dead organic matter; soil; grass-like

Species Richness

the number of different species found in the community. Number of species of most taxa varies according to geographic range. VARIES WITH LATITUDE

Peninsular effect

the number of species decreases as a function of distance from the main body of land.

Currently, about ____ of the tropical rain forests are destroyed each year.

2%

Realized niche

Actual set of environmental conditions, presence or absence of other species, in which the species can establish a stable population

Pioneer Seral Stage

The initial sere

Holistic concept

a community is an integrated unit; superorganism - more than the sum of its parts

Individualistic concept

a community is nothing more than an aggregation of species that happen to occur together at one place. most ecologists favor this today

Human activities that cause the greatest disturbance to communities include:

Agricultural development Logging and clearing Mining and farming

Look at figure 58.11

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Look at slide 16 for this chapters slides

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Study 4 hypothesis made by Whittaker

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Intermediate disturbance hypothesis

Communities experiencing moderate amounts of disturbance will have higher levels of species richness than communities experiencing either little or great amounts of disturbance Patches of habitat will exist at different successional stages May prevent communities from reaching the final stages of succession

Fundamental niche

Entire niche that a species is capable of using, based on physiological tolerance limits and resource needs

Causes of niche restriction

Predator absence or presence Absence of pollinators Presence of herbivores

Shannon diversity index (H_s) formula

H_s = -Σp_i * (ln p_i) pi = proportion of individuals belonging to species i ln = natural logarithm Σ is a summation sign

Views of Communities

Holistic (organismic) concept and individualistic concept/model

J. H. Connels Experiment

In 1954, ecologist Joseph Connell conducted an experiment that overcame this problem. Chthamalus stellatus and Semibal- anus balanoides (formerly known as Balanus balanoides) are two species of barnacles that dominate the Scottish coastline. Each organism's ecological niche on the intertidal zone was well defined. Chthamalus occurs in the upper intertidal zone, and Semibalanus is restricted to the lower intertidal zone. Con- nell sought to determine what the range of Chthamalus adults might be in the absence of competition from Semibalanus.

Climax Communities

In succession, the community proceeds through a series of stages until it reaches A STABLE END POINT. remains constant for a long period of time.

Examples of how species in a community can change over time...

Krakatau island Volcanic eruption Fauna changed in synchrony with the vegetation Changes in animals affect plant occurrences; pollination, animal dispersion massive volcanic explosion in 1883 on the island of Krakatau in Indonesia destroyed two-thirds of the island, originally 11-km long and covered in tropical rain forest. Life on the remaining part was eradicated, suffocated by tens of meters of red-hot ash. Nine months after the eruption, the first reported colonist was a spider spinning its web. By 1896, there were 11 species of ferns and 15 species of flowering plants, mainly grasses. Most plant species at that time had been wind or sea dis- persed. By the 1920s, 40 years after the original eruption, birds had become abundant and had dispersed additional plant species via their seeds.

Why does species richness increase with increasing area? / Area Hypothesis

Larger areas usually contain a greater diversity of habitats and thus can support more species.

Example of Holistic Concept

Organismic model by Clements

Species Richness is reduced by

Peninsular effect

principle of species individuality

Robert Whittaker stated that each species is distributed according to its physiological needs and population dynamics; that most communities intergrade, or merge into one another gradually; and that competition does not create distinct vegetational zones. Supports Individualistic

DIversity Index most used

Shannon diversity index (H_s)

Niches of organisms

Space utilization Food consumption Temperature range Appropriate conditions for mating Requirements for moisture and more

Keystone Species

Species whose effects on the composition of communities are greater than one might expect based on their abundance. Example: Sea stars

How Sea Stars are a keystone species...

Starfish eat barnacles, allowing other species to thrive instead of being crowded out by the explosive population of barnacles

Conclusion of Connells Experiment

The data from this study indicate that Semibalanus is found on the lower rock face because it outcompetes Chthamalus. Other studies indicate that Chthamalus occupies the upper rock face because it is more resistant to desiccation.

Succession in Marine Ecosystem

The deep dark ocean floor is a: barren, inhospitable environment The disturbance begins when: a large whale dies and sinks to the barren ocean floor.

species-area effect

The relationship between the amount of available area and the number of species present. Area hypothesis - larger areas usually contain more species than smaller areas do.

What happens after whale death:

The whale carcass attracts: many scavengers and decomposers that begin to feast on the decaying carcass.

Pioneer Species

These are the organisms that are generally the first to colonize the area.

Species Diversity:

This is the relationship between the number of species in the community to the relative abundance of each species.

Hypothesis' Regarding Species Richness

Time, Area, Productivity, and Intermediate Disturbance

Tolerance vs Facilitation vs Inhibition

Tolerance - species replacement is unaffected by previous colonists Facilitation - species replacement facilitated by previous colonists Inhibition - species replacement is inhibited by previous colonists

The mechanisms/dynamic concepts in process of succession and disturbance

Tolerance, Facilitation, Inhibition

When only skeleton of whale remains

a third community moves in. Heterotrophic bacteria begin to: decompose oils inside the whale bones, releasing chemical compounds that can be used by: chemosynthetic bacteria.

Disturbances

an event, such as a storm, fire, flood, drought, overgrazing, or human activity that changes a community by removing organisms from it or altering resource availability is common, rather than exceptional in many communities

Community

assemblage of many populations that live in the same place at the same time. Species that occur at any particular locality. Characterized by: Species richness Species diversity

Habitat Destruction

by an ever-growing human population is occurring at a faster and faster rate each day, and it can reduce land area.

Inhibition

changes in the habitat caused by one species inhibits the growth of the original species. early colonists prevent colonization by other species.

At low rates of disturbance

competitively dom- inant K-selected species would outcompete all other species, which would also yield low species richness.

relative abundance

frequency of occurrence of species in community

Geographic Range changes in Species Richness

generally increasing from polar areas to temperate areas and reaching a maximum in the tropics. influenced by topographical variation.

Example of Individualistic Concept

individualistic model by Henry Allan Gleason.

Organismic model by Clements (58.1)

individuals, populations, and communities have a stable relationship to each other that resembles the associations found between cells, tissues, and organs. has predictable and integrated associations of species separated by sharp boundaries

Lichen

is the mutualistic relationship between an algae and a fungus. are usually the first to colonize these barren areas.

Community ecology

is the study of how groups of species interact and form functional communities.

In secondary succession, the disturbance has

left the existing soil intact

Pioneer Species have adaptations that

make them well suited to invading and occupying a new area. for example: they may be very good at seed dispersal, or have adaptations that allow them to withstand harsh conditions.

Keystone Species can also be helpful by

manipulating the environment in ways that create new habitats for other species. Example: the beaver, a relatively small animal, can completely alter the composition of a community by building a dam and flooding an entire river valley.

Shannon diversity index (H_s)

measures the diversity in a community. Higher the value, the greater the diversity. Values range for real communities falls between 1.5 and 3.5

at high levels of disturbance

only colonists that were r-selected species would survive, giv- ing rise to low species richness. This is because these species would be the only ones able to disperse quickly to a highly disturbed area.

The organisms in each stage of succession alter the __________________ in ways that make it ____ favorable for themselves but ____ favorable for the organisms that follow.

physical environment; less; more

Reducing the size of a habitat =

reducing the number of species it can support

Primary succession often occurs very ______ because:

slowly; the minerals necessary for plant growth are unavailable.

Pioneer Species tend to be

small, fast growing, and very fast at reproduction.

Succession happens because

species alter the habitat and the resources available in ways that favor other species entering the habitat

Primary succession

succession on a newly exposed site that was not previously occupied by soil and vegetation. Open water and Rocks. a bare rock, a sand dune, or an island formed by volcanic eruption. Only a tiny proportion of the Earth's surface is currently undergo- ing primary succession..

Secondary succession

succession on a site that has already supported life but has undergone a disturbance. organisms still remain the replacement of species that follows a disturbance in an already existing community.

Time Hypothesis

suggests communities diversify with age. Temperate Regions less species rich vs tropical because temperate regions are younger than tropical (the tropical regions have recovered from glaciations and severe climatic disruption)

chemosynthetic bacteria

support a diverse community of: mussels, snails, worms, crabs, and clams.

succession

the gradual and continuous change in species composition and community structure over time. communities tend to change from simple to complex. Organisms gradually move into an area and change its nature two types: primary and secondary

Facilitation keeps happening until

the most competitively dominant species has colonized, when the community is at climax.

Niche

the total of all the ways an organism uses the resources of its environment

Within a year, most of the whale's ______ will have been _____ and only a much smaller community of organisms can be supported.

tissues; eaten

Over time, rocks will begin to break down due to __________

weathering