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Part 4
Biological Surveys
 

 

Biological Surveys

Biodiversity surveys are undertaken to find out what organisms exist in a given area. The data that is gathered from these surveys is used for numerous purposes such as:

  • monitoring endangered populations;
  • evaluating conservation priorities of an area;
  • bioprospecting

Museum and herbarium specimens provide a valuable record of the location of organisms but such data are rarely systematic and often subjective. This is why field surveys are so important.

Despite their importance in biodiversity research, there are no well-defined rules as to how to perform such surveys. This is due to the vast differences between surveys in terms of the goals of the survey, of available resources and time, the area to be surveyed, the organisms to be found, and a myriad of other factors that change from survey to survey.

Still, there are some basic questions that must be addressed before any survey is begun and these questions are explained below.

What are the objectives of the survey?

The survey's objective must be determined: Do we want to inventory the species in a given area? monitor the populations already known to exist there? model the processes driving diversity in the system? These are all valid scientific objectives for carrying out a biodiversity survey. Since it is likely that only a sample of the actual diversity of an area can be surveyed, the goals of the survey are extremely important to ensure that the results are useable.

The objective will guide the answers to the next most important questions: what kind of diversity will we look at and how will we measure it?

What kind of diversity are we measuring?

Genetic diversity

Some argue that the fundamental unit of biodiversity is the gene. Genetic diversity is the degree of variability of the genetic material of an organism (Williams et al. 1994b). Species are defined by the differences in their genes. High genetic diversity indicates populations that can more easily adapt to changing situations and environments, and also a greater assortment of materials that can be found, increasing the chances of finding a useful compound.

However, exact assessment of genetic diversity is both time-consuming and prohibitively expensive, requiring modern laboratories and expensive chemicals. We have so far been able to account for all the genes in just one species of bacteria! Realistically, investigators could only examine a minute fraction of the genetic diversity to be found using this approach, and time is often a constraint.

Species diversity

Fortunately, genetic diversity can be estimated by species diversity, and this has become the standard unit of measurement in most biodiversity surveys.

fern species survey at Mt. St. HilaireSpecies have the advantage of being natural biological divisions and easily identifiable; their diverging appearances were the basis by which they were classified in the 18th century, and modern phylogenetic techniques more often than not produce species divisions similar to those of classical taxonomic divisions. For many groups of organisms, such as birds and flowers, public interest means that identification of many species is already known by large numbers of people.

The degree of genetic variability at the species level, and indeed at any taxonomic level, can be maximized by taking species that differ by one another by as many characters as possible. If these characters represent different genetic elements, then the divergent species should represent greater genetic diversity.

Higher taxon diversity

In the case of some groups of organisms, such as insects, the numbers of species is so large that it is not practical to identify them all. Fully half of the 1.5 million identified organisms are insects. Furthermore, species of many microorganisms have not yet been identified or named. Only identification to higher taxonomic groups, such as to the genus or family level, may be necessary or even possible.

This method works well up to families (Williams et al. 1994a), if the species observed are more or less similar. If the species are quite different this method is less useful, since diversity would be underestimated. Ecological questions can best be answered by these data if the species within the higher taxonomic groups live in similar habitats and pursue similar lifestyles, so that each group can be considered as a relatively homogenous set (Danks, 1997). If the intent of the survey is to generate a list of which particular species are to be found in an area, then this method is unsuitable; conversely, if simply estimating the number of species to be found is the aim, this method is acceptable (Dobson, 1996).

Indicator groups

Sometimes, indicator species may be used to select areas as priorities for conservation and protection because it is assumed that if a given indicator organism is protected, then a number of other organisms may be protected as well.

Using the presence of indicator species as representative of many species can make a survey less costly and time-consuming. However, the complexity of most ecosystems makes it unlikely that any one (group of) organism(s) can serve as an indicator of community structure and function. Indicator groups must be used cautiously at any time, especially when the relationship between the indicator group and the target group is negative; it may be that the two simply live in different locations that are not usually found together at the scale of previous surveys. If the goal of the survey is to establish some cause and effect, then the indicators may not provide the same relationship between the cause and effect as the target groups. Furthermore, setting conservation goals based on indicator organisms may result in the inadvertent loss of species that were not adequately protected (Amanda Vincent, pers. comm.).

Surrogate environmental measurements

To estimate the number of species in an area, surrogate measurements, such as net primary production for plants, may be used, which, although crude, are readily available. The major problem with this method is that specific species are not identifiable by this method, so that estimates of total diversity may be generated, but not the particulars. This method works best for larger areas, where the effects of local differences and chance are minimized.

Methodology: How will the survey be carried out?

The actual methodology of the survey depends the goal of the project, the unit of biodiversity being measured, and how the data will be analyzed. Data collected can be either qualitative (presence/absence, also known as binary) or quantitative data, in which the number of individuals for each species are counted. Small mobile animals such as insects are usually captured using traps or nets, while plants are usually visually identified in the field.

Standardization

Assuming that the data are to be compared or analyzed, sampling for a survey must be kept consistent, not just between different surveyors but also from site to site and day to day. Standardization ensures that differences between sites are significant and not the result of uneven sampling. One way to standardize is by making sure that the species are being correctly identified, by having an outside expert identify the specimens. Should the survey be a noninvasive one dealing with visual identification in the field, the expert identification may be performed on vouchers, which are samples of species that are collected in the field. Replication, taking multiple samples in a site, can also help identify irregularities in one surveyor's technique or among different surveyors.

Sampling Effort

Determining the sampling effort is important and difficult, because it requires a balance between time and effort and interpretability of data, assuming that not all organisms in the area can be correctly identified due to time and labor constraints.

Sampling effort can be expressed many ways: as search time per site, as search within a given distance of a reference point or line, or as total number of sites or replicates needed to find a pattern. For example, the Audubon Christmas Bird Counts will select one 24-hour period where investigators will try to find as many breeding species in an area as possible within 24 hours. Setting a definite time limit also allows the survey to be more standardized and results can be compared from year to year. For a survey to be considered scientific, it must be random; that is, the sites should be selected independent of factors such as the number of organisms found at a site or proximity of a site to the laboratory; although these seem to be valid reasons for spending more effort at a site, this only serves to make the sites unevenly sampled with the end result that differences in diversity between sites cannot be convincingly attributed to something other than the difference in sampling effort.

Scale

The scale at which the survey will be done depends upon the goals of the project and on the unit of biodiversity being used. The scale should be appropriate to the organisms being surveyed; a one-meter scale would be ineffective for full-grown trees, whose bases are often greater than a meter in area; it may be a good choice for ferns. A large scale may also be needed for motile organisms, such as caribou, or large oceanic fish, which have a much larger habitat.

Sampling grids

Large areas may be divided into biogeographic regions or landscapesampling ferns within a grid: Mt. St. Hilaire types, but conducting surveys along these categories is problematic because of the differing sizes of regions or landscapes, especially when the variation within them is examined, or when sharp boundaries must be delineated (Haila and Margules, 1996). Therefore, biodiversity surveys are usually performed using a grid of some sort, as the diversity of an area is usually what is of concern. Point data are not as useful because they are not consistent and the diversity at a point depends upon chance encountering of aggregations. Linear measurements are rarely useful because most patterns of biodiversity are two- or three-dimensional.

A grid should cover the entire area of interest and aggregates of the shape used should form the same shape to allow different scales to be easily compared. Squares and hexagons are the most often used shapes, their dimensions making it simple to sample in one quadrat without inadvertently wandering into another. Grids superimposed over large areas may have problems due to the curvature of the planet (making some quadrats bigger or smaller than others), and so equal-area or almost equal-area grids are used, where the grid is modified such that every quadrat has the same area, although the shape may differ somewhat (Atlas Florae Europaeae).

(Haila and Margules, 1996)

Monitoring

Monitoring is a special type of survey used extensively in conservation work. Monitoring involves repeated surveys of an area over time, which allows examination of effects of change through time as well as of change through space. In fact, the implementation of long-term monitoring of forest ecosystems, St. Lawrence River ecosystems and species at risk is one of the major aims of the Québec Biodiversity Strategy. Monitoring programs are being set up all over the world and span from regional surveys (e.g. Mont St. Hilaire) to global ones (see World Conservation Monitoring Centre website).

Quantitative data are better for monitoring, as they allow changes in the population to be measured, instead of the population simply being recorded as present or absent; it would be helpful to know if a population were in danger before it disappears. Knowledge of the population structure is also very important in conservation, so sex ratios and ratios in different life stages are also needed, which is possible if quantitative measurements are made. Monitoring allows research into not just changes of population size and structure, but also ranges of variation in population size and structure.

Frequency of surveys

The frequency of monitoring depends largely upon the goals of the project and the life history of the species; population changes that may be the result of regular cyclical fluctuations may appear drastic if the cycle is not known. In Canada, population cycles of many larger animals follow a 10-year period while those of small herbivores and their predators follow a 4-year period (Ricklefs, 1990). Consideration of such natural cycles is important to the monitoring of populations.

To prevent an area from being overly disturbed, surveys should not repeatedly sample the same areas, but some area should be sampled in the subsequent survey as well, so that observed changes can be separated into the degree to which they result from sampling new areas and the more universal changes that have occurred since the last survey.

This section was written by Torsten Bernhardt

 

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Part 3: Patterns and Processes of Biodiversity