Examination of the Repeatability and Resolution of Qualitative Sampling Techniques In

Roxanne S. Beltran

October 8, 2011

EXAMINATION OF THE REPEATABILITY AND RESOLUTION OF QUALITATIVE SAMPLING TECHNIQUES IN DETERMINING THE DISTRIBUTIONS OF SELECTED SPECIES AT HOPKINS REEF

INTRODUCTION

One of the goals of ecology is to gain a broader understanding of the community structure, diversity and dynamics of biological communities. This can include examining predator-prey interactions, determining which trophic levels regulate populations, recognizing the effects of resource limitations on competition, addressing the effects of physical processes, or studying the influence of spatial distribution and habitat structure on behavioral patterns (Sala and Graham 2002).

Community structure depends on both the interactions between organisms in the community and the physical nature of the habitat. Regularly observing species abundances and examining distribution over time is critical to maintain a baseline understanding of the distributional patterns of biota in the absence of disturbance factors such as extinctions, sea level variations, changes in climate, ENSO events, etc. The effects of the presence of disturbance factors on distributional responses can then be examined and understood (Reed and Foster 1984, Edwards 2003, Ebeling et al. 2005).

Explanations for the distribution of a particular species vary in every specific case, and can relate to habitat geography (i.e. environmental potential for polygamy) or to the distribution of other species in the region (i.e. partitioning of resources by competition). Distributions can have an important impact on reproductive fitness or on resource acquisition, and therefore on adaptations and on a broader scale, evolution(Hallacher & Roberts 1985, Watanabe 1984).

Regular quantitative or qualitative assessments of distribution are important for various reasons. Quantitatively or qualitatively determining the distribution of a species can help shed light on the effects of habitat structure, or the community dynamics between the habitat and the habitat’s species. Distribution of a species is not permanent, as seasonal changes or the fluctuation of available resources can cause an alteration in both abundance and distribution. By sampling regularly, however, scientists can understand the effects of those seasonal changes or resource fluctuations on distribution. Additionally, changes in distribution that are attributed to human impact are imperative in creating management policies and in practicing sustainability.

Giant kelp (Macrocystis pyrifera) forests are often quantatively and qualitatively studied, because of its ecological significance in providing an important habitat for a variety of species. Because of its structure and density of fronds, M. pyrifera is associated with increased recruitment success and increased abundance of associated diversity. Additionally, as a primary producer, giant kelp converts sunlight into useable energy, which is subsequently transferred to consumers at higher levels (Reed and Foster 1984, Graham et al.

In this study, relative abundance of algae, invertebrate and fish species in a kelp forest system at Hopkins Reef was sampled qualitatively in order to understand the benefits and drawbacks to qualitative sampling methods with respect to quantitative sampling.

We will be addressing three questions: (1) Which species seem to be good or poor candidates for qualitative sampling methods? (2) Do distinctive buddy pairs differ in the level of similarity of scoring between individuals? (3) Are there any obvious patterns of species abundances that vary with depth or distance along the meter tape?

METHODS

In order to examine the distribution of 28 target species at Hopkins Reef in Monterey, CA, transect tapes were reeled out due east (90degrees) from the black cable. Buddy pairs surveyed the same portion of reef individually and assessed the relative abundance of target species every 10 meters using the following categories: 1=absent, 2=rare, 3=present, 4=common, 5=abundant. Target species consisted of 9 fish species, 6 algae species and 13 invertebrate species.

In order to examine the dissimilarity of scoring between individuals in separate buddy pairs, we calculated the relative percent difference between buddy pairs as a function of mean abundance (Figure 5). Additionally, we analyzed the variance between buddy pairs per taxa to determine which taxa had a larger component of variance between buddies (Figure 2).

In order to estimate which species seem to be good or poor candidates for qualitative sampling methods, we calculated the percent relative difference between buddies as a function of each individual species of fish, algae or invertebrates (Figure 2).

In order to determine ways in which the patterns of species abundances vary with depth or meter tape distance (Figure 2), we recorded the distance of the meter tape at which each buddy pair began their transect from, and recorded the depth at both the beginning and end of the transect.

We calculated the mean abundance for all species in order to get an approximate baseline count for the distribution of the target species. Additionally, a variance components analysis was performed to determine which particular source (depth, buddy or meter distance along the transect line) was responsible for the largest percentage of variance within the data(Figure 3).

RESULTS

Data was collected and an ANOVA (analysis of variance) test was performed to show the variability among different sources to determine which source had a largest effect on the response variable (Figure 1). Of the three sources of variance in this study (depth, buddy and distance along the meter tape), the distance along the meter tape had a higher percentage of variance (41% variance) than the other two sources(37% for buddy and 23% for depth). A higher percentage of variance suggests that the source had a more significant or more apparent impact on the distribution of the target species.

To test how….make linkages instead of listing results.When divided by taxa, variance components as a function of source showed dissimilar results to one another and, for certain sources in certain taxa, to the calculation of percent variance by source of all combined taxa (Figure 2). While both algae and fish species showed greatest variation in response to altered distance along the meter tape, interestingly, invertebrate species showed no variance with respect to altered distance along the meter tape. Depth had a high level of variance for invertebrates, but a low level of variance for algae. Buddy pairs had a higher level of variance for invertebrates and for algae than for fishes. Give values for statements like this.

Mean abundance was analyzed as a function of species, separated by taxa (Figure 3). These results showed that while species of fish did not vary a great deal in mean abundance, algae and invertebrates did. Algae abundance was much higher in Macrocystis pyrifera and Cystoseira osmundacea, and lessin Pyllospadix spp.Invertebrates varied significantly between species, with Patiria miniata observed to be most abundant followed closely by Balanophyllia elegans, Calliostoma ligatum, Pachycerianthus fimbriatus, Pisaster giganteus and Tethya aurantia reaching between 2 and 3 in mean abundance values. The least common invertebrates reached amean abundance of about 1and includedHaliotis rufescens, Strongylocentrotus franciscanus and Urticina picivora.

Percent variance of abundance between buddies as a function of species was also calculated and separated by taxa (Figure 4). Similar to the results seen in Figure 3, the highest percent variance was seen in invertebrates. The variancebetween buddies did not seem to correlate with the abundance of a particular species (??).In other words, more abundant species did not necessarily have higher variation in qualitative assessments between buddies. Really? What about fig 5?

Lastly, relative percent difference between buddy pairs as a function of mean abundance of species was analyzed (Figure 5). Percent difference between buddies was negatively correlated with mean abundance, meaning that the qualitative assessments of buddy pairs tended to be more similar in the more abundant species.

DISCUSSION

We were interested in determining if qualitative sampling was less resolute or less accurate [jf1]than quantitative sampling.Repeatability refers to the assessment of a system that is repeatedly studied under identical conditions. Resolution is a measure of precision, or the range of positions when a system has high repeatability. Ideal resolution is the smallest possible range of positions with repeatability.

Because two individual buddies in a buddy [jf2]pair sampled from the same transect tape, degree of repeatability was defined as the degree of similarity between individual buddies in this study. Lower repeatability within an observer and between observers may be a consequence of experience observer or subjective interpretation of an estimate. The degree of repeatabilityshould imply something about accuracy, because increased repeatability should allow for increased accuracy in data collection.

Qualitative sampling is probably less accurate than quantitative sampling because the estimates of a variable will tend to not be as accurate as the actual value of the variable. It may also be less resolute, depending on the specific situation. For example, two buddies in a pair who have similar skill levels and experience may be resolute precise but not accurate. In this particular study, buddy pairs were generally similar, especially for species of invertebrates, algae or fishes that are more abundant.

Though the qualitative methods may be less accurate or precise, they allow scientists to gain a general idea of the species abundance and distribution in a time-efficient manner. When scientists are forced to go underwater to collect data, time is precious, and for bigger picture studies rather than small, specific studies, qualitative sampling may be a better method.

Conclusion? Finish with a summary statement about the methods pros and cons. How Is it useful for evaluating trends?
TABLES AND FIGURES

FIGURE 1

FIGURE 2

FIGURE 3

FIGURE 4

FIGURE 5

WORKS CITED

Ebeling, A.W., Laur, D.R., Rowley, R.J. 1985. Severe storm disturbances and reversal of community structure in a southern California kelp forest. Marine Biology 84: 287-294.

Edwards, M.S.(2004). Estimating scale dependency in disturbance impacts: El Niños and giant kelp forests in the Northeast Pacific. Oecologia 138: 436-447.

Graham MH, BS Halpern, MH Carr. 2008. Diversity and dynamics of Californian subtidal kelp forests. Pp. 103-134 in McClanahan, TR and GR Branch (eds), Food Webs and the Dynamics of Marine Benthic Ecosystems, Oxford University Press.

Hallacher, L.E and D.A. Roberts. 1985. Differential utilization of space and food by the inshore rockfishes (Scorpaenidae: Sebastes) of Carmel Bay, California. Environmental Biology of Fishes 12:91-110.

Reed, D.C., and M.S. Foster. 1984. The effects of canopy shading on algal recruitment and growth in a giant kelp (Macrocystis pyrifera) forest. Ecology65: 937-948.

Sala, E. & M.H. Graham. 2002. Community-wide distribution of predator-prey interaction strength in kelp forests. Proceedings of the National Academy of Sciences of the USA 99: 3678-3683.

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 65:920–936.

Results (25)

_0___/4 Figure legends Accurate

_0___/4 Figure Legends well composed (complete and concise)

__4__/5 Results organized according to questions

__4__/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)

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

1)__2__/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)__1__/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

__1__/2 General Thoughtfulness

__2__/3 Clarity and conciseness

__4__/5 Organization of discussion

__1__/3 Context and Bigger Picture

General Notes: Figures need legends.

[jf1]confusing

[jf2]don’t use “buddy” : slang