Dominance has multiple attributes so before deciding on a method to study it you should probably work out which attributes matter most in your application and proceed to an objective function from that starting point. I'd be wary of going straight to an off-the-shelf software solution to begin with until you are certain what it is that you want to know. Getting a precise definition of dominance first, might be very useful?

Neil Mcroberts: " I'd be wary of going straight to an off-the-shelf software solution to begin with until you are certain what it is that you want to know."

may be he has a project-report dead-line... so he has there no time to think about such ""details"

Do you mean dominance in terms of numbers, or in terms of what the species do (functional aspects)? These are two distinctly different questions, that need to be answered in very different ways.

Dominance is a subjective word, with many alternative meanings. For example, a species dominant in number of individuals may be 'rare' in terms of relative biomass in a system.... with different consequences depending upon whether is looking for mass-ratio type effects, or instead population abundances. I would agree with the prior posts and suggest refine the research question first, and then the statistical approach can follow.

Well, first of all, I am interested in theoretical side of this subject which is not clear. For example,I have forest snail sample from point where one medium sized snail X is 95% in number and roughly 90% in biomass of all snail community. Ok, it is clear that X is a dominant in that community. As there are some extreme environmental condition, I can assume that the X can overcompete other snails. This is the meaning of dominance in this case.

Well, I have another sample of forest snails. Where The X is still 90 % in number, but 10% in biomass (as there are several times large helicid snail Y which uses the same resources), and yet another community where the numeric proportion of X=35%, another similar size class snail Z=33%, and in biomass is same not strongly differentiated distribution. it is clear that "most abundant" is a very arbitrary as the small difference can be bias of sampling.

Is it IndVal appropriate choice here?

If the differences (either in number, or biomass, or both) is not enough between first two or more species, maybe there can not be distinguish a dominant(s) ?

Is it good choice to use a null model in this case? as an expectation, null model will produce either significant result that species X is more than expected in specific condition. Dos it means that it is or not a dominant?

thanks for your answers

Hi Levan,

I would recommend a reading on ecological dominance by trophic roles- Robert Payne 1966 in American Naturalist. Maybe it's not directly what you're looking at but I think those discussions from that paper and others following could really help your thought process. Another good ref is Ecology 1984 Robert Payne where he defines dominance by how much of an effect a particular species has just by being present in a community. This would mean their effect doesn't have to be direct for every species but that they also don't have to be the most numerically abundant to be considered the "dominant".

Hope that helps!

I see no problem; but, I see the issue from an observational position. Essentially, the natural history of microbial communities in extreme environments.

Dominant does not mean "superior", it must meet all of the following criteria:

1. It must constitute the largest mass;

2. It must structurally support other species;

3. it must support other species through mutualism;

4. It must be capable of reorganizing the community;

5. And, it may have co-dominant species.

In the San Francisco Bay salt marsh communities, which I study, salinity drives the ecology. Salinity is driven by tides, by influx of fresh water from sloughs and the Sacramento river delta, and by evaporation. Excursions of salinity range from around 10-ppt to salt ponds routinely reaching 150-ppt. All microbial species living in these ponds have roughly bell-shaped growth curves around a salinity of maximal growth. At the salinity of maximum growth rate for a dominant species, the resulting complex microbial mat can reach hundreds of metric tons of mass within weeks. Photosynthesis in such a mat can be so intense that the mat becomes covered with a foam of bubbles.

In one such mat, the area covered grew to about 0.5-sqMile in less than a month, apparently in response to changing salinity of the pond. This was a complex mat with co-dominant community of cyanobacteria and a purple non-sulfer bacteria with gelatinous sheath. The sheath trapped and retained bubbles of oxygen from the intense photosynthesis - floating the mat [which was about 5-cm thick]. At night the mat sank to the bottom of the pond, in daylight the mat rose to the surface. Diatoms swarmed over the filamentous cyanobacteria in some form of mutualism. The total number of "species" supported in this mat community probably ran into the thousands. Three months later, the mat was almost entirely gone.

Some small ponds appear to undergo a regular alternation between a mat dominated at lower salinity by the colonial diatom Melosira and a sheath-making filamentous cyanobacterium at higher salinity.

One such pond alternated for around a year between a mat dominated at lower salinity [~24-ppt] by an unknown species of motile pinnate diatom that formed a complex network of "sheath tunnels" and a motile species of filamentous cyanobacteria that also formed, at higher ppt [~32-ppt], similar-appearing "sheath tunnels".

Badly needed to understand such dynamics are studies coordinated between species tracking by DNA barcoding and detailed observation and measurement physical and biological parameters. Several of us have been carrying out the detailed observation and measurements; but, lack the tools for routing DNA barcoding. Anyone interested at participating at that level would be greatly appreciated. I have developed field microscope tools for collecting small numbers of individual microbial cells.

It's a classical problem, when the community is defined on a taxonomic base, as e.g. opposed to 'feeding guild'. When trying to make statements about dominant competitors or any other ecologically meaningful definition of dominance, you might ignore important imfluences of animals outside of your defined community. So you might want to ask yourself: Why snails?

If it is about the diversity of snails, then dominance (or the opposite: evenness) is simply a part of the measure of diversity.

There is a good review about the consequences of dominance (within the frame of this definition):

Hillebrand H., Bennett D.M. & Cadotte M.W. (2008). Consequences of dominance: a review of evenness effects on local and regional ecosystem processes. Ecology, 89, 1510-1520.

http://www.esajournals.org/doi/abs/10.1890/07-1053.1

Hello,

in a recent paper I have used indicator species package, between communities, or regions, basins etc. In case you are interested I can send you more information

Cheers

Anthi Oikonomou: "in a recent paper I have used..."

where did You up-loaded the pdf to Your personal page from this www-site?

no it is under publication. I have used indicpecies in R

Yes, I want to see your work Anthi

For a first approach to species dominance and cover, I think that the method of line-intercept is enough. Data for species with more individuals, more cover or more volumetric biomass can be obtained easily with some transects (at least in Mediterranean communities).

Try the 'Importance Species Index' (ISI)

ISI is interesting index indeed, however I guess it is not relevant to analyze dominance in one sample for example as it will be in this case just a relative abundance.

https://sites.google.com/site/anthioikonomou87/matrix/analyses see this one, I have uploaded the particular example to see what I am talking about.

Very much will depend on how you define "dominants" - in microbial communities, food webs or plant communities they are very different. They theory on dominants in plant communities belongs to Philippe Grime (Grime, J.P. (1987) Dominant and subordinate components of plant communities – implications for succession, stability and diversity. In: Colonisation, Succession and Stability (eds. A.Gray, P.Edwards & M.Crawley). Blackwell, Oxford, UK, pp. 413 – 428). The idea is that in a healthy plant community most abundant species govern the resources and ecological processes relevant to plant community dynamics. Although subjective, this concept was very useful in guiding research and producing other definitions. The paper you cite in your question presents an "objective" method because its use does not depend on your perception, yet this measure is true only for the definition of dominants used in this paper, that is based on Simpson's dominance index. Other definitions can produce other ways of determining their number.

If by "dominant species" you mean the species whose relative abundance is significantly large in a given area, then you'd have to determine first if the community is highly biodiverse or not through biodiversity indices. Communities that are low in biodiversity are usually governed by 1-2 dominant species. Once you've assessed that a community is indeed low in diversity, you can identify the dominant species through sampling methods. For plants, sessile organisms, and slow-moving animals, quadrat and line transect counts would work, and are efficient in estimating the percent cover and species abundance. For megafauna (or K-selected organisms in general), the stationary point count method can be used. For avians and flying animals, I'd recommend mist-netting. This way, you can analyze the relative abundance of species in a community and pinpoint the dominant species. 

Hope this answer helps!

I study salt marsh microbial communities in the San Francisco Bay salt marsh and desert playas. Because of the interplay of tides and evaporation in these Bay shallow ponds, the members of a community constantly change. Moreover, because the dominant organisms are frequently Archaea and Cyanobacteria, the term "species" is frequently not applicable. When the dominant organism is a colonial diatom, for example, it is rarely useful to determine "species".

As ponds evaporate and recover, I do identify an emerging "dominant member" and sometimes "co-cominant member". The primary factors are: (1) population density; (2) an essential structural role; and, (3) a possible "nutritional" role.. For those few meanders or "shallow streams", where the salinity does not vary greatly, it is possible to define a persisting dominant organism also based on population and structural considerations.

For example, one of the stable communities is found in a drainage ditch of roughly two miles in length in the Don Edwards San Francisco Bay National Wildlife Refuge. It opens at Coyote Creek and ends at the site of the New Chicago Marsh. It is regulated by a weir gate near Coyote Creek which is partially closed during winter rains, but it continuously flows. The dominant population is the colonial diatom Melosira (sp). The upper salinity ranges between a low of about about 10-PPT to around 20-PPT, but rises to the level of New Chicago Marsh at its outlet. Typically the growth of Melosira is greatly diminished as the salinity rises near the outlet. A variety of apparently dependent microorganisms grow among and on the long strands of Melosira, including motile pennate diatoms, many smaller bacteria, and the occasional Cyanobacterial filament.

In contrast, I have studied six small ponds in the LaRiviere Marsh of the Don Edwards Wildlife Refuge. The elevation of these ponds is almost exactly at the mean tidal elevation, so at various times during the year they dry up during very low tides. We have measured salinity and determined populations in the ponds continuously over a span of about 1.5-years. The salinity of these ponds ranges from around 35-PPT to above 250-PPT as the pond drys up. The dominant organism appearing when the dried pond recovers is not predictable from the population at the high-salinity prior to drying up. Frequently the dominant population is some form of filament such as Oscillatoria or Lyngbya. These filamenetal Cyanobacteria are often associated in an apparent mutual relationship with many different diatoms, small bacteria, etc. At least once, however, I have found the dominant organism upon recovery to be a species of small pennate diatom which constructs long gelatinous tubes which act as highways with continuous traffic of diatoms slipping past each other.

The ecology of these salt marsh ponds is highly complex. Even the simplest ecology can still be surprising. At the sand dunes of Trona Reef, in Southern California, lives a species of crust-forming Microcoleus. Although it looks like M. vaginatus, the filaments are smaller in diameter and the crust formed is much thicker and more sturdy. A rough survey showed this crust covered roughly 1/3rd of the dune area in Trona Reef. I collected a sample of this organism and found I could grow it in lighted stirred culture at high salinity. I could not, however, grow it axenically. A small cocci was always present in growing cultures and when I succeeded in removing the cocci, the Microcoleus failed to grow. Clearly a necessary mutualism. The Microcoleus appeared to be dominant, but required the small "fellow traveler".

I have found this in attempting to culture other organisms from ephemeral ponds, playas, and salt marsh ponds. The dominant organism apparently supports a large community of co-dependent organisms - either structurally, or by mutual exchange of nutrients. In time lapse micro-movies, the Cyanobacteria filaments continuously move and moving on and among them are small diatoms and many different species of smaller bacteria. Continued and repeated contact between the "dominant" Cyanobacteria and freely moving bacteria, protozoa, and small diatoms suggest an exchange of essential nutrients. So, it the "dominant species" will not grow in the absence of some clearly "not dominant" species, what does this "dominance" mean...?

Defining "dominant organism" in a complex community must take these issues into account.