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