chapter 16

an associtaion of interacting species living in a particular area; aslo often defind as all the orgainisms living in a partictular area

Guild - a groiup of organisms that makes their living in a similar way; for exapmple the seed-eating animals in the desert, the fruit eating animals of the tropical rain forest, or the filter-feeding invertebrates in a stream

Life form- the life form of a plant is a combination of its stucture and growth dynamics. Plant life-froms include trees vines annual plants, sclerophylbus vegitation and forbs

• •Preston graphed abundance of species in collections as frequency distributions.vLognormal Distributions
• -Bell-shaped curves.

Note the log2 transformed X axis= reflects our suggestive way of quantifying quantities



In most lognormal distributions, only portion of bell-shaped curve is apparent.Sample size has large effect.Significant effort to capture rare species.

•May proposed lognormal distribution is a statistical expectation.•Sugihara suggested lognormal distribution is a consequence of the species within a community subdividing niche space.

Sugihara suggested taht the long normal distriution is a consequence of the species within a commiuinty subdividing niche space. regardless of its origins. the lognormal distribution is important because it allows us predict the distribution of abundance amoung species

in most normal distrubutions, only portion oa a bell shaped curve is apparent. prestion sugguested that much of the difference between the 2 curves results from a different sample size. ecologists have found that the more u sample a commuinty, the more species you will find. the common species show up in even small samples, but a great deal sampling effort is needed to capture the rare species

Missing rare

must have 60% of the curve can estimate the rest

species richness- the number of species in a commuinty or collection.

species eveness- the relative abundance of species in a community or collection.

Pielou index-

0>E> 1 (eveness)

• •Shannon Wiener Index:
• H’ = -Σpi Ln(pi)

• i=l
• •H’ = Value of SW diversity index.
• •Pi = proportion of the ith species.
• •Ln = natural logarithm of pi.
• •S = Number of species in community.

• Problem of H’:
• - do not know the size of the sample (you might miss the rare spp)
• - do not know the richness or the evenness. ---- estimate rarefaction based upon the lognormal distribution can help.

rank-abundance curves- a curve that protays the number of species in a commuinty and their relative abundane; constructed by plotting the realtive abundance of a species against thier rank in abundance

Greater evenness indicated by lower slope.







Flat = high eveness

Steep = flow eveness

• more niches => more diversity = more species richness

• *the competivie exclusion principle leads us to predict that coexisting species will have significantly different niches
• *his results suggest that since these spices forage in different vegetative strata, thier distributions may be influneced by varition in the vertical structure of vegetation.

• * he explore this possiblity on Mount Desert Island Maine, where he measure the relationship between volume of vegetation above 6m and the abundance of warblers .
• * the number of wasbler species at the study sitea increased with the forest stature. the sites with greater volume of vegetation above 6m supported more warbler species . in other words he found that warbler diversity increased as the stature if the vegetation increased.

* he was one of 1st ecologists to quantify the relationship between species diversity and environmental heterogeneity.

• * used the shannon-wiener idex
• - found that his foliage height diveristy , like species diversity, increases with richness( the # of vegetative layes) and eveness ( how evenly vegetative biomass is distibuted amoung layers)

* plant commuinties with greater foliage height diversity supported more diverse bird commuintes

* he suggest that communites of phytoplankton present a paradox because the live in relatively simple enviroments ( the open waters of lakes and oceans) and compete for the same nutrients (nitrogen, phosphorus, silica, etc), yet many species can coexist without competetive exclusion.

* this situation is paradoxical because because it appears to violate the competetive exclusion principle.

*he grew the diatoms Asterionella formosa and Cycotella meneghiniana by themselves, they established and maintained stable populations

* when he grew them together Asterionella sometimes excluded Cycotella and sometimes the species coexisted.

• * the outcome depended upon the ratio of silicate to phosphate
• - at high ratios Asterionella eventually excluded Cycotella.
• -at lower ratios the 2 species coexisted
• - at the lowest ratios Cycotella was numerically dominate over Asterionella

• * it turns out that the Asterionella takes up phosphorus at a much higher rate than does Cycotella . he reasoned that at high ratios of silicate to phosphate Asterionella is able to deplete tha enviroment of phophorus and cansequently elimante Cycotella
• - when ratios are low. silicate limits the growth rate of Asterionella and it cannot deplete phosphate. consequently when ratios are low, Asterionella connot exclude Cycotella . at these low ratios, silicate limits the growth rate of Asterionella while phosphate limits the growth rate of Cycotella. consequently, in the presence of low ratios of silicate to phosphate , the 2 diatoms coexiste.

from the prespective of plants and algae, variation in the availability of limiting nutrients such as silicateand phosphate and the variation in physical and chemical conditions such as temperature, moisture and pH, contribute to enviromental complexity

*proposed that disturbance is a prevelent feature of nature that significantly influences the diversity of communities.

* questioned the assumption of equilibrium conditions made by most competition-based models of diversity.

* he proposed taht high diversity is a consuqunec of continually changing conditions, not of competitive accommodation at equilibrium and proposed that intermediated disturbance hypothesis, which predicts that intermediate levels of disturbance promote higher levels of diversity

*suggested that both high and low level of disturbance would lead to reduce diversity

* reasoned taht if disturbance is frequent ans intense the commuit will consit of those few species able to colonize and complete their live cycles between frequent disturbances

* predicted that diversity eill decline if disturbance are infrequent and of low intensity


* in the absence of significant disturbance, teh community is eventually limited to the spescies that are most effective competitors, effective either because they are the most effiecient at using limited resources or the most effective at interference competition

* suggested taht at intermediate levels of disturbance there is sufficient time between distrubance for a wide varirty of species to colonize but not enough time to allow competitve exclusion

commuinty structure - attributes of acummnity such as the number of species or the distrubition of individuals smoung species within the commuinty

equilibrium- the state of balance in a system in which opposing factors cancle each other

species diversity -a measure of diversity thst increases with species eveness and species richness

* most species are moderately abundan; few re very abundant or extremely rare

* a conbination of the number of species and their relative abundance defines species diversity

* species diversity is higher in complex enviroments

* intermediate levels of disturbance promote higher diversity