BIOLOGY Volume 2 - A Guide to General Biology - 2004

11. QUANTITATIVE ECOLOGY

11.2. Analysis of Biota

When studying the organisms inhabiting a given habitat (the biotic component of an ecosystem), it is necessary to characterize the community Structure, i.e., its species composition and the population sizes of different species. Obviously, finding and counting every individual in a population is not always feasible; therefore, specialized sampling Methods have been developed that do not always require the direct recording of every single Organism. In general, the higher the required accuracy, the more time must be spent to achieve it. Consequently, It is important to clearly define your objectives in advance. Furthermore, whenever possible, methods should be employed that do not disrupt natural communities.

In any case, reliable recording (tallying and/or collection) of organisms is essential. Since they occupy every conceivable microhabitat, surveying an area requires literally turning over every stone (just make sure to put them back afterwards!). At first glance, a square meter of meadow, sand, rocky shore, or riverbed may seem to be inhabited by a rather monotonous biota. However, by carefully sorting through the soil, closely examining plant shoots, roots, flowers and fruits, algal mats, or clumps of pond scum, you will almost certainly discover far more species than expected.

When recording data, you should strive to identify as many encountered taxa as possible directly in the field using specialized identification guides. Only if a species is clearly not rare in that Location (and globally) should a specimen be removed from nature for further laboratory analysis. The excessive zeal of collectors has already caused serious damage to many communities. If an animal is captured, every effort should be made to keep it alive so that it can subsequently be released back into a similar environment. Organisms should be identified as accurately as possible, i.e., down to the species level. This is not always achievable, but you should always aim for the lowest taxonomic rank accessible to you—Class, order, or family. The identification of each organism depends on your ability to use dichotomous keys. The principles of using them (and the principles of biological Classification in general) are discussed in detail in sections 2.15 and 2.16.

A list of all identified species in a given habitat provides a General Overview of community structure, allowing for a rough estimate of its species richness and diversity. (Various formulas have been proposed to calculate these parameters, which we will not discuss here.)

The assemblage of species provides insight into FOOD CHAINS AND food webs, but says nothing about the Quantitative Aspects of the community. The most adequate indices of biotic diversity for comparing ecosystems are calculated precisely by taking into account the number of individuals of each species, i.e., their population sizes. In addition, quantitative data make it possible to construct ecological pyramids (sec. 10.3.4).

All of this information depends on the methods used to collect it, and the methods, in turn, are determined by the lifestyle, behavior, and size of the organisms.

11.2.1. Methods for Sampling Organisms

When surveying (remotely counting, collecting, or trapping) organisms in nature, A number of rules should be followed, as outlined below.

1. Always observe safety protocols. Naturally, these rules depend on the object and conditions of your study. Discuss this matter in detail with an experienced field biologist before beginning fieldwork.

2. Always comply with local environmental regulations and land-use practices.

3. Protect the ecosystem in which you are working. Strive not only to avoid damaging it, but also to prevent any lasting alterations associated with your presence.

4. Before initiating any ecological study, be sure to obtain permission from the landowner.

5. Consult with local conservation organizations, universities, angling and hunting associations, etc., regarding where and what you are permitted to study and collect.

6. Avoid destroying organisms or removing them from their natural environment unless absolutely necessary.

7. As much as possible, leave the studied habitat undisturbed: return any displaced rocks, logs, etc., to their original positions.

8. If it is necessary to remove organisms from the environment for identification, limit yourself to the minimum number of specimens and make every effort to return them alive to their habitat.

9. Animals captured for laboratory identification should be kept individually to prevent them from harming one another—for example, do not place worms in the same container as crabs. Suitable collection containers include ordinary screw-top jars, plastic bottles and bags, test tubes, and the like.

10. Always record as much physical and geographical information as possible about the collection site and the prevailing weather conditions. Particularly important factors include:

a) parent material and substrate (mud, soil, grass, etc.);

b) surface characteristics (e.g., flat, south-facing slope with a gradient of X degrees, etc.);

c) soil or benthic sediment profile;

d) drainage;

d) substrate, Water and air Temperature;

e) substrate or water pH;

f) cloud cover and precipitation;

g) relative air humidity;

h) illumination (at least visually, but if possible, measured with a light meter);

i) wind speed and direction;

j) date and time of day.

An example of a standard data-recording sheet is shown in Table 11.2.

There are numerous methods for collecting (trapping) animals. An Overview of these methods is provided in Table 11.3, and some types of equipment used are illustrated in Figs. 11.5–11.10. Collected specimens must be removed from traps at regular intervals, identified, counted, and released whenever possible. Keep in mind that predators and prey may end up in the same trap simultaneously, leading to an undercount of the latter. If this probability is quite high, a destructive sampling method must be used—i.e., killing the animals immediately, for example, by pouring alcohol into the pitfall trap container. In general, any census method requires ingenuity and resourcefulness.

Sampling sites are rarely chosen at random; therefore, results should always be interpreted with caution, keeping in mind that they may deviate from the habitat's "average" parameters. Even if the species COMPOSITION OF THE community is represented quite thoroughly, its quantitative characteristics will likely be "skewed." The sampling method itself also affects the results (e.g., catching insects with a sweep net versus attracting them to sticky traps). Consequently, when discussing collected data, one should always account for potential reasons for their deviation from the true state of affairs.

Table 11.2. Field data sheet for recording soil, physical, geographical, and climatic parameters

Table 11.3. Summary of various organism collection methods

Fig. 11.5. Simple pitfall trap made from a glass jar buried in the ground.

Fig. 11.6. Mercury-vapor light trap for catching insects.

Fig. 11.7. Small mammal trap (Longworth live trap).

Fig. 11.8. Tullgren funnel.

Fig. 11.9. Baermann funnel.