Variance in Data for Qualitative Sampling

Monica Chu

10/11/11

BioE161/L

Variance in Data for Qualitative Sampling

Introduction

Information about the abundance and distribution of different species allows researchers to determine factors affecting the coexistence of the species being studied. (Watanabe, 1984) Knowing these factors and how species coexist helps to understand the overall health of the community – whether one species is dominating the other all over the area or not. Thus, to learn as much as possible to maintain ecosystems of all kinds, it is necessary to study the areas and collect data. Data can be collected in a multitude of way, but it comes down to whether the data collected is qualitative or quantitative. Quantitative sampling deals with multiple surveys to collect statistical evidence to create an objective analysis and tends to be more generalizable across an area. On the other hand, quantitative sampling involves unstructured or semi-structured reviews that use the inductive process to come up with a subjective analysis that may only apply to the area surveyed. In this study, the kelp forests of Stanford’s Hopkins Marine Station were studied, using SCUBA, to determine the distributions of selected species. In thisstudy, buddy pairs will differ in their data when doing qualitative sampling because this style of sampling is very subjective, and may depend on level of skill and rigor. Specifically for this site, it seems that fish, like the striped surfperch, Embiotoca lateralis, are not a good candidate for sampling using qualitative methods; however, invertebrates, such as the bat star, Asterina miniata, do make good candidates for qualitative surveys. This is most likely because there are so many bat stars down there; so the divers have an image to compare the other inverts to. As for the fish, they are not a good candidate because they are so widespread that a diver may only see one and write that down as rare; yet, the species is known to not be rare.

Methods

Research was conducted at Stanford University’s Hopkins Marine Station in Pacific Grove, CA. In pairs, divers swam out to a buoy, descended and swam to specific meter marks. Each pair had a different mark and took a heading offshore, at 270 degrees; and swam in that direction while unreeling a meter take until 30 meters. As they unreeled and swam, each diver observed and made mental notes about what was present and in what abundances. After the 30 meters were reeled out, each diver wrote down, on a scale of 1 to 5, with 1 being absent, the abundances of what species they observed. After writing down their data, they turned back and swam the oppsite way back to their start point doing the same thing for that leg. After one transect was complete, pairs did another transect, using the same method, to survey that meter mark going onshore, 90 degrees. After this, data sheets were collected and compiled to create graphs for analysis.

Results

Within[jf1] a buddy pair, there seems to be a lot of disagreement in abundances of fish, and invertebrates, except in Sebastes chrysomelas, Haliotis rufescens, Strongylocentrotus fransiscanus, Urticina piscivora, and Urticina lofotensis – in these species, relative difference was below 20%. (Fig. 1) For all algae species, there was a relative difference above 20%.

It seems there is a lot of confusion ???? as to whether or not a species was present or absent. All species except Macrocystis pyrifera and A. miniata have a disagreement species don’t have a disagreement between buddies below 20%, specifically at 0%. (Fig. 2) For fish, algae, and invertebrates, the species with the highest percentage of relative disagreement are Embiotoca lateralis, Dictyoneuropsis reticulate and Pachycerianthus fimbriatus. (Fig. 2) Link your ideas here.

With all the data compiled, it appears that there is a trend when assigning numbers to the species. There was[jf2] the least relative difference between buddies when assigning a number 5, and the most relative difference when assigning a 2. (Fig. 3) Good

Figure 1: Relative difference (%) and species based on rank data taken by 19 buddy pairs at Hopkins Marine Station, Pacific Grove, CA. Good but be more clear about relative difference of what???

Figure 2: Disagreement between buddies (%) and species on presence or absence of the species based off data from 19 buddy pairs at Hopkins Marine Station, Pacific Grove, CA.

Figure 3: Relative difference (%) between buddy pairs as a function of mean abundance of species.

There are some figures that Pete gave you that would have been useful in the results

Discussion

There will be at least some disagreement between buddies when conducting qualitative surveys – this is something that cannot be prevented unless what each number, 1 through 5, should correspond with how many individuals of a species is discussed beforehand This is a very awkward sentence. In this study, what each number meant, other than the terms absent, rare, present, common, and abundant, was not discussed.

It is possible that the reason behind the species with the least relative difference is because these species are very easy to identify. The black and yellow rockfish, red abalone, red sea urchin, fish-eating urchin, and white-spotted rose urchin are indeed very easy species to identify. These species also tend to not be found with others of the same species, except red urchins, so it is possible that these species were not very common out in the transects.

This area has otters, Enhydra lutris, often; so they most likely control the population of sea urchins, which allows the kelp to grow very large. (Davenport and Anderson, 2007) This may be true, but it distracts from your argument. Why would rare species show less differences in the ranking between observers?

For the presence or absence of species, the large disagreement for most of the species except three is likely due to the diver’s skills or observational skills. One buddy do not use buddy ( observer) could possibly be looking around for certain species while the other was just looking for what was around and catching his eye.

The fact that the least percentage of disagreement occurred when assigning a number 5 for a species as abundant makes sense because bat stars, for example, were everywhere and they was????? impossible to count one by one. This provided divers a number to base off of – if a species was not as numerous as A. miniatus, then that species did not receive a 5. Really, would you rank species against other species or against other samples?

Overall, the large disagreement for the majority of the species’ abundances proves to me that the qualitative method is inaccurate an unreliable when trying to study trends in species. I believe that trends must be taken quantitatively so as to project over a wider expanse of area other than just the study site (How?). This would allow better data to be collected to use as a better understanding of how these species are coexisting and the overall health of the kelp forests could be better understood. Are there benefits to qualitative??

Works Cited

Davenport, Andrew and Anderson, Todd. 2007. Positive indirect effects of reef fishes on kelp performance: the importance of mesograzers. Ecology. 88(6): 1548-1561.

Watanabe, James M. 1984. The influence of recruitment, competition, and benthic predation on spatial distributions of three species of kelp forest gastropods (Trochidae: Tegula). Ecology. 65(3): 920-936.

Results (25)

__3__/4 Figure legends Accurate

__3__/4 Figure Legends well composed (complete and concise)

__3__/5 Results organized according to questions

__3__/4 Graphs presented in a logical order, case made for the order

__3__/4 Grammar, sentence structure and spelling

___3_/4 Clarity and conciseness of writing

Discussion (25)

_5___/9 How well did they answer the questions they present in the Intro?

1)__1__/3 Discuss the results from the specific to the general.

2)__2__/3 Do these results surprise you? In other words, is the qualitative method more or less reliable than you thought it would be, and do you think that degree of reliability (which can be assessed based on relative difference between buddies) implies anything about accuracy?

3)__2__/3 Do you think the qualitative sampling approach is appropriate for describing trends of species abundances through time? Explain your answer

__2__/3 Grammar and Spelling

_2___/2 General Thoughtfulness

__2__/3 Clarity and conciseness

__3__/5 Organization of discussion

__1__/3 Context and Bigger Picture

General Notes: Present your questions and NO results in the intro. Structure the rest of the paper around those. Write concisely! Be careful not to write in the same way that someone would talk. Draw linkages between the results and spin your “story” from there.

1

[jf1]Be definitive in your statements. Seems like…..is not good

[jf2]There was is a wordy way to start a sentence…..be concise. Trim out unnecessary word.