Katelyn Laird
Bio 161/L
M. Carr and P. Raimondi
Total score: 71/100
Title [[4/4 – nice job getting the “so what” in there while also including the important information. You could additionally include the fact that the study is of invertebrates and algae, but it works pretty well as is.]]
Using interspecific and species-habitat associations to explore niche diversification theory in kelp forest habitat
Clarity [[10/14 –Overall your writing is pretty clear, but try to cut out the unnecessary words because you sometimes use about twice as many words as you need and it obscures the points you’re trying to make. Also, you REALLY need to work on organizing your ideas so that they tell a coherent story. Try outlining them and then finding the big points and pulling them up to the top so they direct your reader.]]
Introduction [[15/20 – this has many of the right elements and you do a good job of introducing the broad ecological context, but you don’t use nearly enough references and examples. You do a nice job of connecting your specific questions to the broader ecological context, but again could use more references. Also, nice nod to the novelty of the study and relatively good description of why this system is well suited to this kind of study.]]
The maintenance of species richness in habitats containing high levels of biodiversity is a complex process determined by many physical and biological factors, and is frequently undergoing ecological study. Because of the process of evolution, one would expect that the best adapted competitors of an ecosystem would out-compete all other species, the resulting of which would bein a significant decrease in the variety diversity of species seen in the composition of thatin the ecosystem. The subsequent decline in biodiversity would occur most severely in habitats with limited resources, where the highest rates of competition exist (Connell, 1964). [[good intro to broad ecological context , but more references and information needed!]]
The substantial biodiversity that is observed in many ecological communities despite limited resources and high rates of competition indicates that there must be some mechanism in place that effectively facilitates the survival of species that are not considered the top competitors. This mechanism is likely complex, involving an abundance of species and habitat interactions, and therefore will continue to require more study to be fully understood. Past hypotheses have suggested that some habitats have greater biodiversity because they have more niches to be filled, or that regions with greater biodiversity have become that way over a long period of time, and that regions with less biodiversity have simply not yet matured as far (Connell, 1964). However, these theories have lost support as further studies have been made. [[if you’re going to say this, you need to explain why and what the competing theories are – more references and examples needed]]
One possible mechanism, niche partitioning, has been studied at depth and may be a necessary part of ensuring the continued survival of these less-fit species. When environmental resources are finely partitioned between species, competition amongst these species is subsequently decreased, and resources are used more efficiently.
We conducted observational studies to address the question of whether or not niche partitioning is occurring amongst species associated with the benthic zone of the kelp forest ecosystem. This study was unique in that we used two different survey methods to observe the same area of habitat, and linked the data from both surveys to describe abiotic and biotic characteristics of the habitat [[nice]]. The kelp forest is an excellent place to study maintenance of species diversity because of its high level of biodiversity and limited resources. Species recruit to this habitat at high rates and take advantage of the nutrient-rich waters, however, the limitation of other kelp forest resources, particularly space and light, leads to high rates of competition. Whatever mechanism is maintaining biodiversity in the face of this competition is effective in this ecosystem, or a handful of species would be out-competing the rest [[a little awkward wording, but I like that you are presenting evidence that SOMETHING is maintaining diversity in the face of heavy competition]].
If niche partitioning is the mechanism at work here, we would expect each species to have a strong set of associations with physical and biological characteristics of their environment that is unique in at least one element from that of every other species living in similar habitat. [[Nice explanation of how your study is motivated and how it connects to the broad ecological questions]] To see if this is occurring, we looked at species’ individual associations and determined whether or not there were associations between species and their physical habitats, and between benthic species and each other. This question is of particular interest because such associations describe species’ fundamental and realized niches. I expect that there will be associations both between species and their habitats, since species determine where they will live based on their physical requirements, and interspecifically, since interactions with other species can facilitate or hinder survival success, or even result in a species’ mortality.
If these associations do occur, then a second question we wish to address with this study is whether or not the associations between species and their habitats have a different strength than associations between species and their biological communities. I predict that habitat associations will be more influential than species associations since associations with habitat are often the result of species’ biological and physiological requirements for survival and of their behavior as larvae and as adults, including patterns of recruitment, settlement, feeding technique, mating and reproduction. I expect that associations with UPC species [[need ot describe what the UPC species are]] composition will also be influential, since they are the result of direct and indirect interspecific interactions, but will not have as strong an effect on species composition. I expect these associations to reflect relationships of mutualism or commensalism, where species are benefitted by being in close proximity, or to reflect shared habitat preference.
If associations exist, we would also like to look for evidence of particular patterns among observed associations, for example, correlations occurring between swath species and UPC species that differ in strength between swath species, despite a preference for identical habitat features. Such observations would support the likelihood of niche diversification occurring, since they would illuminate the slight differences between species that otherwise appear to share the same niche. I expect to see variation in association patterns from species to species, but I predict that interspecific associations will follow predictable patterns based on known predator-prey relationships and the existence of competition. [[this explanation of specific questions and hypotheses is a bit longer than needed for the intro, but you have the right ideas here]]
Methods [[14/18 – this section would really benefit from some subheadings to separate ideas and make it easier to read. You’ve got most of the right stuff in there, though, it’s just a little hard to find.]]
To study whether niche partitioning is a mechanism facilitating maintenance of species diversity in kelp forest habitat, we conducted two distinct observational studies along a permanent cable at Hopkins Marine lab in Monterey using Uniform Point Contact and Swath survey sampling techniques, respectively. With the Uniform Point Contact method, we characterized benthic habitat in terms of substrate type, size of relief and primary substrate holder at discrete points along a 30-m transect. UPC survey method is suitable for describing substrate and species relative abundance of species when abundance is too great to be able to count individuals. [[good]]
We implemented a swath method for the second survey to collect data about the abundance and composition of species in a 30m x 2m transect. [[explain this more]]
The site at Hopkins was ideal for these surveys because of the existence of the permanent cable that allowed us to execute the two studies along the exact same transect and therefore gather data on separate days, and with different methods, that could later be linked because of its geographic consistency. Since the cable runs parallel to the shore, each survey could be repeated at an offshore (referred to as ‘deep’) and an onshore (‘shallow’) heading. This site also contains high levels of biodiversity and possesses a varied physical environment in terms of substrate and relief, making it ideal to study the variation in associations between species and their habitat.
The reef is made of granite, which provides solid substrate for species to bind to, and the area is protected from the biggest swells, so many species settle there. Since space is limited, competition is high, increasing the necessitation for a mechanism to maintain biodiversity and adding to the appropriateness of the site as a place to answer our overall question about the maintenance of species richness. In addition, Hopkins usually has decent visibility, making it suitable for observational studies. [[don’t’ forget the importance of habitat and species diversity for answering your questions]]
To explore the question of whether or not niche diversification is occurring in this ecosystem, we tested the hypothesis that there are associations between species and features of their environment. Our first hypothesis asks if there are associations between species and habitat and our second hypothesis asks if interspecific associations exist. To test both, we gathered sets of data describing species abundance and statistically linked this data to data describing types of habitat features and the biotic composition of the species’ surroundings. If no discernible patterns of associations are seen, we will not have evidence that would support rejecting the null hypothesis, which states that there are no associations between species and habitat or between species and each other. [[this seems to work]]
If interspecific associations differ in strength from species-habitat associations, habitat and biota may have varying roles in determining species’ fundamental versus realized niches. To test the hypothesis that associations between species and habitat have a different strength than interspecific associations, we compared habitat-species associations and interspecific associations using a Bray-Curtis dissimilarity matrix. The null hypothesis states that there is no difference in strength between interspecific and species-habitat associations.
To determine how niches are being interspecifically partitioned, we tested the hypothesis that strengths and patterns of association vary from species to species, by using statistics to extract the relative strengths of associations from the data and compare them from species to species. The null hypothesis states that there is no significant variation in associations from species to species. [[you could structure this section a little more clearly, but you have most of the right pieces of information]]
[[a subheading about data collection methods would be good here]]
Both the UPC and swath surveys were conducted by a group of twenty divers working in pairs. Each pair was assigned a different mark along the permanent cable at which to begin laying out a transect tape. These buddy pairs and the assigned mark along the cable of each pair were the same for both surveys, so that divers’ sampling techniques would be as consistent as possible between the two data sets. The UPC survey was completed April 10, 2012, and the swath survey was done a week later on April 17, both at approximately the same time of day.
To conduct the UPC survey, each diver pair laid out a transect line from their cable mark along the offshore 90º heading and followed this line while observing and recording the substrate type, relief size and primary substrate holder at points directly below the tape at every half-meter mark. The two divers were staggered with a 2-meter interval to conduct the survey.
Substrate type was categorized as sand, cobble (<10 cm), boulder (10 cm-1 m) or bedrock (>1 m). Relief size was categorized as flat (0-10 cm), shallow (10 cm-1 m), medium (1 m- 2 m) or high (>2 m), with the recorded relief being the deepest point in a square meter around the point, including any cracks or crevices. The primary substrate holder was most closely in contact with the point. Divers moved algae or detritus out of the way if another organism resided below it, and recorded the organism in closest proximity to the substrate. The 33 UPC primary substrate holders included 15 invertebrates, 14 algae and 4 other materials. After both divers had reached the end of the 30-m transect, the tape was rolled back up and laid out from the cable again, this time along the onshore 270º heading, and the survey was then repeated along this transect. The UPC survey resulted in twenty sets of data, one set for each offshore or onshore transect and two transects for each pair of divers.
The swath survey was identical in terms of diver distribution along the cable, and divers again used a 30-m transect tape. However, for this procedure, each pair of divers swam out from their position on the cable side by side, simultaneously rolling out the tape and observing and recording species. The survey was performed in 5-m increments, starting with the 0-5 meter distance along the tape. Each diver observed species composition along a 1-m distance extending out from the tape on their respective side, resulting in a 2-m x 5-m area from their combined observations for each section. After the divers observed all six sections of the 30-m tape and recorded the species composition of each, the divers rolled the transect tape up and returned to the cable. The pair then repeated the procedure to the 270º heading, with each diver on the same side of the tape that they were on during the first transect.