Field Report #1: Qualitative Sampling
The effects of buddy variance and species selection on qualitative sampling
Kristen Brown
BIOE 161: Kelp Forest Ecology
ABSTRACT:
Ecology is the study of the relationships between living organisms and their interactions with their environment. Knowing the distribution and abundance of organisms within a community is vital for understanding ecology. In kelp forest ecology, sampling techniques are utilized to provide insight to the ecology of underwater world. Qualitative methods were tested in comprehending the effects of buddy variance and species selection on the accuracy of the scientific process. Variance Components Analysis revealed that qualitative sampling is neither accurate nor precise.
INTRODUCTION:
One of the goals of kelp forest ecology is to recognize factors affecting the cohabitation of species within a community and to understand how these patterns impact distribution and abundance (Watanabe 1984). Determining the distribution of species within a community is crucial to understanding the interactions between organisms and the physical nature of the environment. It can provide insight into predator-prey interactions occurring within the community (Sala and Graham 2002). It can help us examine recruitment patterns and how that affects dispersal and species richness (Watanabe 1984).Competition for resources such as light (Reed and Foster 1984) and food (Hallacher and Roberts 1985) can also be observed to lend understanding into community dynamics.Knowing what species occur where and in what proportions can be useful in rebuilding a community following a physical or ecological disturbance.
Sampling a community can be done using a variety of techniques which can be categorized into two methods: qualitative and quantitative. Each method has advantages and disadvantages, and where one lacks, one can make up for it. Qualitative is useful if time and resources are limited. Unfortunately, as this study shows, it may not be the most precise or accurate. Precision can be achieved using quantitative sampling techniques, however it requires more time in training and more time underwater. Also, more resources need to be allocated such as additional tanks possibly accompanied by a boat and sampling gear for examplequadrats, meter sticks, and random point contact (RPC) chains.
In our study, we utilized qualitative sampling methods to determine if two individuals of a buddy pair fluctuate in their data collection. We aimed to determine if qualitative sampling is at least likely to be accurate. Possible differences in recordings can be attributed to: connotation of words used in scoring, diving experience, familiarity with the dive site, and knowledge of the species being sampled. In the species chosen for this study, some were better candidates for qualitative sampling, while some were worse. The poor candidates are species that are cryptic, camouflaged, and small. Oppositely, better candidates include species that are abundant, bright, and big.
METHODS:
The field studies were conducted using SCUBA in the Hopkins Marine Station in Pacific Grove, CA (Figure 1). Large granite benches in shallow water yield to high relief protrusions surrounded by shell fragment rubble in deeper water (Gerard 1976). Shallow areas have high cover of small benthic algae and a high turnover rate of Macrocystis, where deeper areas have significantly lower cover of algae, individual plants are smaller, and Macrocystis turns over less often (Watanabe 1984).A permanent transect cable runs roughly north (0⁰) to south (90⁰) along the bottom.
Fourteen pairs (28 individuals) were assigned various positions corresponding to specific meter marks along the transect cable.To help explain variance within buddy pairs, each individual had their own data sheet consisting of 28 different species of algae and plants, invertebrates, and fishes (Table 1).One dive was made on the deep (west, 270⁰) and shallow (east, 90⁰) sides of the transect cable. The relative abundance of species were recorded for 30 meters in both directions of the deep (270⁰) and shallow (90⁰) sides of the cable (for a total of four legs).The time at start and finish, the depth at start and finish, and visibility/conditions were also noted. Each individual conducted their own survey of the environment without comparing information in order to determine differences in scoring. Comparisons of the data were made by variance components analysis to measure compatibility between pairs in amounts of species, among other data recorded.
[jf1]RESULTS:
Variance components analysis revealed a few key results. Overall, variance was attributed to three sources: depth (meaning the shallow versus deep side of the cable), buddy, and meter marks (Figure 2). In order of most to least variance, meter had the most (about 40%), followed closely by buddy (about 37%), and lastly depth (23%).[jf2]Figure 3 depicts variance components by taxa. Looking specifically at algae (Figure 3a), we see the same results conveyed in figure 2 with meter variation reaching approximately 52%, buddy about 38%, and depth around 10%. Fish (Figure 3b) showed the most variance in meter at around 62%, while discrepancy in depth (22%) is higher than that of buddy (17%). Invertebrates, however, revealed curious results with all variance split evenly 50/50 between buddy and depth.
Relative difference between buddies separated by taxa, and further by species is shown in figure 4. We see most inconsistency in invertebrates (Fig. 4c), followed by algae (Fig. 4a), and closely by fish (Fig. 4b). Relative difference between buddy pairs as a function of mean abundance of species is conveyed in figure 5[jf3]. This graph is skewed to the lower valued side, peaking at two (about 73%), which corresponds to ‘rare’.Three or ‘common’, is followed in highest percentage of variance (about 45%).
DISSCUSSION:
Figure 2 shows the meter marks had the most variance. This is expected as specific environments along the transect can differ greatly, especially at Hopkins Marine Station (Figure 1). Algae variability was due largely to meter marks, as was fish (Figure 3a, 3b). However, invertebrates had no variance in meter marks. This result is interesting. I believe this may be because there is an even distribution and abundance of this taxon throughout the site.
Buddy [jf4]variance followed meter marks closely. In order to produce accurate results from a survey, you would want the smallest amount of buddy variance, if any at all. However, shown in figures 2-4, we see that this is not the case. No two people are identical and because of this, no buddies will score identically. Variances within buddy pairs are due to any number of reasons. Differences in diving experience in a similar temperate kelp forest environment will produce discrepancies. Persons who are unfamiliar with species names, morphology and normal abundance may not record accurately. Being well acquainted with the dive site will produce more precise results. Additionally, conceptions of some words such as ‘rare’ and ‘present’ can all lead to inconsistencies in scoring. I deduce that if ‘rare’ and ‘present’ were combined into one category, buddy variance would have decreased (Figure 5).
The third source of variance, depth, was the smallest. Certain species have depth, food, and habitat preferences, and will be found where there needs are met. Invertebrates had the greatest depth fluctuation (Figure 3c). Wantanabe (1984) showed that Tegula have certain depth stratifications and habitat preferences, supporting our findings.We should expect some amount of variance in depth, because the species do differ when moving from shallow to deep.
Species that are enticing are desirable for qualitative sampling. Bright and big species fascinate divers and make them notice their presence. Invertebrate species such as Pycnopodia helianthoides and Urticina lofotensis sampled in our survey prove this hypothesis by displaying a smaller amount of buddy variance (Figure 4c). Also, rare or cryptic species can be desirable for a qualitative survey. Invertebrate species such as Haliotis rufescens and Strongylocentrus fransicanus showed little buddy variance (Figure 4c), probably because they weren’t seen and therefore placed into the only category with no perception issues- one, or absent. Fish move. Because of this, they either move away from you, you don’t see them, and you don’t count them, or they move towards or near you, you take notice, and record them, species that are large, colorful, and cryptic such as Sebastes chrysomelas showed little buddy variance [jf5](Figure 4b). For algae and plants, Macrocystis pyrifera is undoubtedly the easiest to sample in a qualitative survey because it isgiant, hinders your movement, and is the most apparent. Cystoseria osmundacea also showed small amounts of variance (Figure 4a), possibly due to its unique structure.
Species undesirable for qualitative sampling include smalland sessile species. Ballanophyllia elegans is the perfect example, showing over 50% buddy variance (Figure 4c). Tethya aurantia and Pachycerianthus fimbriatus also support this hypothesis (Figure 4c). The algae Dictyneuropsis reticulata also shows over 50% variance, possibly because it is sessile and relatively small (Figure 4a). None of the fish, however, show over 50% buddy variance (Figure 4b). Again, supporting my hypothesis, fish are motile and distinguishable fish are generally larger. Or is that pattern driven by the sheer lack of fish….so divers all recorded 0.
The results of this study are what I expected to find. The qualitative method has proven not only inaccurate, but not precise in this case. It has been unreliable. Buddies have too many discrepancies, as discussed above, which leads to results skewed by human error. I believe if this study were to be repeated with qualitative methods, accuracy and precision would increase. However, this survey provided a general, but not precise, overview of the population at this site. Because of this, this method can be used as an appropriate technique in describing trends of species through time. If time and resources are limited, it is more beneficial to have a general idea of what the population was like at that time, as opposed to no information at all.
REFERNCES:
Gerard, V.A. 1976. Some aspects f aterial dynamics and energy flow in a kelp forest in Monterey Bay, California. Dissertation. University of California, Santa Cruz, California, USA.
Hallacher, Leon E., and Dale A. Roberts. 1985. Differential utilization of space and food by the inshore rockfishes (Scorpaenidae: Sebastes) of Carmel Bay, California.Environmental Biology of Fishes 12.2: 91-110.
Reed, Daniel C., and Michael S. Foster. 1984. The effects of canopy shading on algal recruitment and growth in a giant kelp forest.Ecology65.3: 937-48
Sala, Enric, and Michael H. Graham. 2002. Community-wide distribution of predator-prey interaction strength in kelp forests.Proceedings of the National Academy of Sciences 99.6: 3678-683.
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: 920-36.
Results (25)
__3__/4 Figure legends Accurate
__3__/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
__2__/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)__3__/3 Discuss the results from the specific to the general.
2)__3__/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
__2__/2 General Thoughtfulness
__2__/3 Clarity and conciseness
__4__/5 Organization of discussion
__2__/3 Context and Bigger Picture
General Notes: Overall, well done. Be careful to not get into every detail of every species in the discussion. Organize the discussion around the main points that you want to make. Figure legends should be more complete – think standalone.
1
[jf1]Figure legends should be more complete….variance of what?
[jf2]These 3 sebtebces can be combined to one. Focus on being concise.
[jf3]Reference figures like you did the others…not like this.
[jf4]Don’t use “buddy”. Maybe observer instead.
[jf5]Avoid nouns used as adjectives. Variation among observers…..