Ecology Is the Study of How Different Species Interact with Each Other and How They Are

Introduction

Ecology is the study of how different species interact with each other and how they are connected to their environment. In order to discover how they relate, we must first learn which species inhabit the same area. The distribution of a species informs us about where a species prefers to live, and abundance tells us how many individuals there are. Distribution and abundance are vital pieces of information to begin piecing together species to species interactions.

Distribution begins with the environment a species needs to survive and includes both abiotic and biotic factors. Abiotic factors include sunlight, water temperature, pH, nutrient levels, water movement and depth. These inform us about what type of environment allows for the survival of a species. Biotic factors include interactions such as availability of prey, protection from predators and ability to reproduce. A species can only survive if it has prey to feed upon and protection from predators. The hunt for prey usually includes competing with members of other species, interspecific competition. For example, Sebastes chrysomelas (black and yellow rockfish) and Sebastes carnatus (gopher rockfish) are virtually identical species of benthic rockfish which live and hunt on the floor of the kelp forest. However, S. carnatus occupies the productive shallow zone, forcing its sibling species S. chrysomelas into the deeper sections of the kelp forest floor which contains less prey and more predators. When S. carnatus is removed from the community, S. chrysomelas moves quickly to fill the niche. Thus interspecific competition plays a large role in the distribution of these two species (Hallacher &Roberts, 1985). Competition is driven by species seeking a similar habitat to capture prey and avoid predators. It inevitably results in aggressive actions to intimidate or physically harm the competing species. Competition can continue indefinitely unless one species retreats, which influences its distribution. Mutualistic interactions can occur where two species occupy the same physical area but benefit one another. Fish such as Oxyjulis californica (Senorita) remove parasites from fish that come to get cleaned, benefitting both species (Coastal Fish Identification: California to Alaska).

The abundance of a species is indicative of how successful it is in finding an appropriate niche. This is determined by the same biotic factors that determine distribution. However, there is a difference between surviving in a location and thriving in a location; that difference is measured by abundance. A species with high abundance is successful enough in an area to produce many offspring, and many offspring lead to high abundance. High reproductive rates can also lead to an increase in distribution, as offspring that survive can scatter and enter new communities.It is important to remember that the term abundant is relative to each species. A common benthic invertebrate such as Patiria miniata (Bat Star) would not be considered abundant if only 5 individuals were seen on a dive in Monterey Bay, California. However, to see 5 Enteroctopus dofleini (Pacific Giant Octopus) on one dive would mean that species is incredibly abundant in that area, as it is a rare and shy individual.

In order to determine distribution and abundance, data must be gathered and cataloged to measure both qualities. The ocean is a difficult place to conduct science, for beneath the surface we cannot breathe, see, smell, hear or move normally. Data gathered in a kelp forest must be done so by scientists trained in the use of SCUBA equipment, and time is limited by air consumption. Therefore, time is of the essence, as a limited number of dives may be conducted in one day. The tradeoff then becomes gathering more data in a rapid manner or gathering less data more thoroughly. These are qualitative and quantitative surveys, respectively.

Qualitative surveys include descriptions of variables as opposed to a measurement of variables. Data taken is recorded within general categories. The Great American Fish Count trains divers to positively id fish species on a dive and record their abundance. Fish abundance is recorded within the categories of single, few, many and abundant. Divers swim freely throughout the dive site of interest. This type of survey is easy to learn as it requires no precise measuring and requires very little equipment. One survey can be completed quickly, so a large amount of data can be gathered in a short period of time. However, qualitative surveys are very general and as a result of that precision is lost. Divers may also differ significantly in categorizing relative abundance of species, leading to biased results. Statistical tests are not run without accounting for this bias.

Quantitative surveys are conducted through measuring variables, and therefore deal with numbers as opposed to categories. Data taken is recorded as the number of times a subject of interest was encountered. The Partnership for the Interdisciplinary Studies of Coastal Oceans (PISCO) measures the numbers of fish, algae and invertebrate species as well as recording substrate data. Abundance is recorded as the number of times a certain species was seen on transect. This survey is more difficult as it necessitates exact measurement and gear is required to do so. Swell and visibility are factors to consider as more difficult conditions can lead to incorrect measurements. Quantitative surveys also take more time than qualitative surveys. However, data gathered by well-trained divers is precise and statistical tests can be used to compare diverse sites in a completely unbiased manner.

To answer the overall goal in determining which method of surveying is the best approach, the following questions must be addressed. Are you looking for a question or an answer? Qualitative surveys provide questions but rarely hard answers; quantitative surveys can provide both. Are you assessinga large ecosystem or a small community? Qualitative surveys can be conducted by one individual in order to minimize bias, and so small communities can be reasonably measured qualitatively. The more individuals involved means an increased potential for bias, so larger spatial zones are better analyzed by more divers using quantitative methods. Are you interested in broader ecological questions or spatial and temporal actions by one species? Large scale ecology is generally formed off observations by scientists, therefore qualitative methods are generally used. However to support observations, quantitative methods must be conducted to validate a hypothesis. When observing a species, the characteristics which the species contains determine whether qualitative or quantitative methods should be used. Species that are highly visible by foraging in the open or containing vibrant coloration are good objects for qualitative surveys. Divers with less training will procure similar results to divers with more experience because species are easy to spot. Species that are more difficult to find, less noticeable or more prone to being shy should be counted quantitatively. Researchers need to have similar training and methods in order to generate an unbiased data set on distribution and abundance of the species of interest.

An important determinant of whether qualitative or quantitative methods are appropriate is how reliable the estimates are. Reliability can be measured by repeatability or precision, which can be determined by comparing data collected by one buddy pair. Observers sampling the same habitat should produce similar estimates, as they are seeing the same thing. Lower variability indicates reliable methods, while increasing variability reflects the opposite. Unless observers were trained improperly, quantitative data collected should always be reliable, as long as environmental conditions cooperate. Qualitative data, on the other hand, has potential to be unreliable. Observers with variable levels of experience can be more or less comfortable underwater. A less comfortable diver will spend more time focusing on not dying, which means less time spent observing, procuring a less accurate data set than their more experienced buddy. Observers with specialties in different fields can spend more time focusing on their specialty than looking at the big picture, which is the point of quantitative surveys. Divers can have different expectations for abundance of species as well as varying exposure to species diversity in the area. A buddy pair diving along a meter tape are swimming next to each other, and therefore seeing two different views of the substrate and benthic species. Any of these occurrences are enough to skew a data set and make it unreliable.

Methods

Surveys were conducted using SCUBA between the depths of 5 and 15 m at Hopkins Marine Life Refuge. Hopkins is located about 200 m downcast of the Monterey Bay Aquarium in Pacific Grove, CA. Shallow areas (0-6 m) are composed of large granite benches with high cover of small turf algae and high turnover of Macrocystis pyrifera (giant kelp). Deeper zones (8-13 m) contain high-relief pinnacles encompassed by shell rubble in deeper water. The deeper sections have significantly less turf algae cover with lower turnover rate of Macrocystis and higher density of understory kelps such as Pterygophora (Watanabe 1984).

One dive was conducted in the late morning of September 27th, 2011. Observers were arrayed in 5 meter increments along the permanent main line on the Hopkins Reef. Divers conducted one deep transect rolling out the meter tape for 30 m along a 90 degree heading, gathering qualitative data both rolling out (leg 1) and rolling back in (leg 2). The process was repeated on the shallow side of the main line along a 270 degree heading for legs 3 and 4. Visibility was recorded, as well as depth at the main line and at the end of leg 1 and 3. Total dive time was logged upon clipping in to the main line, at the end of each leg, and upon beginning ascent.

Observers were given access to data sheets prior in order to ensure proper identification of 28 species of algae, fish and invertebrates common in the area. Buddy pairs were not formed until the morning of the dive, and buddies were not allowed to discuss how they were going to score for abundance. This ensured that buddies would be autonomous in scoring, although they were diving along the same transect and therefore surveying the same area. To quantitatively estimate abundance species were recorded in 5 levels of abundance, with a score of 1 for absent, 2 for rare, 3 for present, 4 for common and 5 for abundant.

Results

Hopkins reef show greatest variation along the length of the main line (Fig. 1).

Fig 1. Variance component analysis. Variance as a percent (Y axis) of three sources, depth , buddy and meter mark along main line (X axis).

The largest differences in the data came from the observers’ location along the reef, whereas depth did not prove to be a huge factor(fig 1). Fish were the most variable along the length of the meter tape (Fig. 3), with algae nearly as variable (Fig. 2). Interestingly[jf1], there was zero invertebrate variation along the length of the line (Fig. 4). However, variation in the abundance of fish and algae variation was high enough to make observer location on the reef the primary source of overall variation. Depth, determined by the shallow or deep side of the main line, created high variancefor only invertebrate species. Of the taxa sampled, invertebrates had the highest number of more abundant species (Fig 7), followed by fish (Fig 6) and then algae (Fig. 5). Since species names are written in code, I will go over the species present. Of the invertebrates, Patiria miniata was the only common species, with Pisaster giganteus

Fig. 2, 3, 4. Variance components by taxa. Y axis is measured in percent variance and X axis is the source of variance, buddy, depth or meter mark.

(giant spined sea star),Pachycerianthus fimbriatus (sand anemone), Calliostoma ligatum (ring topped snail), Balanophyllia elegans (cup coral) and Tethya aurantia (orange puffball sponge) also present.

Fig 5, 6, 7. Mean abundance of algae, fish and invertebrates sampled. Y axis is the score for abundance (1: absent, 2: rare, 3: present, 4: common, 5: abundant). X axis is code for individual species.

Algae

Fishes

Invert

Fig 8, 9, 10. Presence/absence data. Percent disagreement between buddies for algae, fish and invertebrates sampled. Y axis is % disagreement (one buddy said yes, the other no) and X axis is species.

Haliotis rufescens (red abalone), Strongylocentrotus fransiscanus (red urchin) and Urticina lofotensis (white-spotted anemone) were marked as absent. All fish species were considered rare, with Sebastes carnatus and Sebastes chrysomelas absent.Cystoceira osmundacea (chain bladder kelp) and Macrocystis were common, with Dictyoneurum californicum, Dictyoneuropsis reticulatum, and Chondracanthus corymbiferus marked as rare.

Data varied immensely between buddy pairs, showing a greater amount of overall variance than depth. Highest variance between buddies was seen for invertebrate species, second highest for algae specimens and least for fish. Differences in buddy pairs resulted in the most prominent source of variance for inverts (50%!). The only species that showed low variance (less than 10%) between buddy pairs were S. chrysomelas, Cystoceira, Macrocystis, H. rufescens, P. miniata and U. lofotensis (Fig. 8, 9, 10). Only Macrocystis and P. miniata showed zero disagreement between buddy pairs.

Discussion

The large variation between meter marks shows that Hopkins reef is diverse and contains many different habitats along the length of the main line. This is supported by the high variance of fish and algae along the reef.Invertebrate data shows zero variance along the line, which could mean that the whole reef provides ample habitat for the various species we searched for. Another possible explanation is that 30m is enough of the reef to view many different species of inverts. Invertebrates, however, show much higher variation between shallow and deep zones than fish or algae. From my own personal observations, I can say that the shallow transect contained much more Styela montereyensis (Stalked tunicate) and Pachycerianthus fimbriatus (sand anemone) while having a much lower density of P. miniata.

The shallow zone contained (as stated in the methods section) much more turf algae and more sandy patches, ideal habitats for the two species mentioned above. The length of the reef is fairly high relief, which leads to rubble slopes, ideal places for benthic fish species to hide. High variance in algae along the meter marks provides different habitats for midwater fishes, further increasing fish diversity across the reef.

Differences between data taken by buddy pairs were also a major source of variance in the data. Buddies showed the most variance with invertebrate species, slightly less with algae and little with fish species. Out of the inverts that were actually present on transect, only P. miniata showed little variance (H. rufescens and U. lofotensis showed abundance scores of 1: absent. The same situation holds true for S. chrysomelas). The highly abundant and visible algae species Cystoceira and Macrocystisalso showed low variance. All three of these species are easy to recognize, abundant, and distinct.

All fishes besides S. chrysomelas show high levels of variance. One possible explanation is the divers were not well trained enough to distinguish between fish species. Another possibility is that fish, as mobile individuals, were scared by one diver while their buddy did not get the chance to notice their presence. S. chrysomelas is quite possibly the most distinct of the species sampled with its vibrant coloration. Since all divers could easily spot and identify this rockfish, it allows for a significantly lower score of variability between buddies. The data also shows that S. chrysomelas scored only slightly higher than 1 on abundance, meaning that the low variance between buddies could also be due to its scarcity.

The algae species D. californicum and D. reticulatum scored extremely high on variance levels between buddies, followed closely by Phyllospadix spp. The two aforementioned species are both very similar to one another, which could explain buddy variance. The data sheet also had D. reticulatum incorrectly written as Dictyoneurum reticulatum, which could be another source of discrepancy.Macrocystis, mentioned before, [jf2]showed no variance between buddies.

We can see that the species that are easily recognizable and abundant make the best candidates for qualitative surveys, as evidenced by variation in buddy data. This means that buddies with different levels of experience will procure the same results for a selected few species. However, there are factors which may disqualify a species from qualitative surveys due to loss in precision. A species that contains similar characteristics to another can be difficult to accurately ID. Species that are not common in an area or that achieve high abundance with low numbers of individuals are seen only by a few divers out of a group. Organisms such as Oxylebius pictus (painted greenling) or Loxorhynchus crispatus (masking crab) can be so well camouflaged with their environment that they escape detection, even when present in high numbers. S. fransiscanus and H. rufescens find refuge in cracks and crevices, and only observers searching thoroughly with a flashlight will discern them.

A vast majority of species of interest within a kelp forest fit one of the disqualifying parameters above. This does not mean that quantitative surveys should never be used; it simply means that observers need to be trained in order to rule out possibility of incongruity. However, training divers rigorously in qualitative methods can be less rewarding as data gathered is still general and therefore harder to run accurate stats on. Quantitative surveys require more training and preparation but control for many of the factors that make qualitative surveys unreliable. The hard data gathered by these methods can be used to run statistical tests which can answer questions about both long and short term distribution and abundance which gives clues to larger ecological questions.