Project Amazonia: Monitoring - Fauna

Bioindicators

Ideally, one would be able to monitor the health and population dynamics of every species in a particular ecosystem.  However, when discussing the Amazon rainforest, this is impossible.  The biodiversity of the rainforest is such that not only are there vast numbers of species contained within, but many of them are very rare or endemic to the Amazon region.  Therefore, in order to efficiently characterize the fauna of the rainforest, a different method must be used.

One such way is the use of bioindicators.  Bioindicators are species that are particularly sensitive to the environment, and provide information about ecosystem health.  Indicator species respond well respond both to the presence or absence of other species as well as the presence of pollutants.  By studying the population dynamics or by statistically sampling an indicator species, one can deduce much information about the rest of the ecosystem?s health.

There are three kinds of bioindicators:

a) compliance indicators:  these verify that maintenance or restoration goals have been met

b) diagnostic indicators:  these help the investigation of observed disturbances

c) early warning indicators:  these reveal the first signs of a disturbance before most species are affected 

In an attempt to cover all three types of indicators, we selected two groups of animals to serve as indicator species: bats and amphibians.  Based off scientific papers, it was decided that bats would serve as good indicator species because they have an abundance of species, occupy almost every trophic level, contribute to ecological processes such as seed dispersal and pollination, and because they select specific habitats¹.  The first three reasons make them good bioindicators, the last reason makes them easy to monitor.

Amphibians were selected because they take in nutrients through their skin, so toxins in the environment build up faster in their bodies than in other species.   For instance, if someone is using a certain pesticide, we can monitor the frogs of the area and test them to see conclusively if a decrease in population is resulting from exotoxicity.  This proves that the pesticide is having a negative effect and should be removed.  Similar experiments may be done to determine pollution by industries, such as mining or logging, or any other possible source of contamination.

There is a slight difference between bioindicators and key indicator species.  While both of them are useful in deducing information about their environment, bioindicators tell us information about the environment through their population numbers or particular responses to the ecosystem, while key indicator species are those species that are essential to an ecosystem.  That is, if such a  specie were to disappear, a good part of the food web (indeed the whole ecosystem) could perish.  A good example of key indicator species is the connection between otter, sea urchins, and kelp.  If the otter were to disappear, there would be no species to eat the sea urchins, and their populations would grow as their food source, kelp, would disappear faster and faster.

As it applies to the rainforest, however, monitoring key indicator species to find out information on the ecosystem is not very efficient.  That is, with such biodiversity, it is almost impossible to find a key indicator species.  There are such vast numbers of species, and the Amazon food web is so complex that if one species were to disappear, the other species can quickly adapt.  Every species in the Amazon consumes many different species, and is likewise consumed by many different species, therefore a key indicator is not readily apparent.

Bats

With increasing human encroachment on the Amazon rainforest and its diverse faunal constituents, monitoring its impacts on the habitat and ecosystems becomes proportionally more imperative. Though satellite imagery, soil sampling, water analysis, and detailed air sensory may give researchers an idea about the general health of the habitat, the information provided by these techniques would not give a very clear picture of how human encroachment is impacting the animal life of the rainforest. Due to the sheer mass and diversity of the rainforest, it would be extremely difficult and probably completely unfeasible to attempt to monitor all of the animals that exist in the Amazon rainforest.  Here is where indicator species come in: due to their inherent characteristics, preferred habitat and place in the food web, indicator species are extremely sensitive to the overall health of the rainforest's ecosystems. By monitoring the progress of these species over time, researchers are able to easily determine whether or not an ecosystem is being affected by unusual or adverse conditions. One particular type of animal that has been selected to be a primary indicator species is the bat. Bats are relatively easy to monitor due to their commonplace occurrence in every trophic level in the canopy, and their relative immobility which results from maintenance of a permanent roosting place. They are also significant contributors to the ecology of the rainforest, helping to maintain insect populations, pollinating flowers, and dispersing seeds over broad areas.

Bats¹ are of the order Chiroptera, which is divided up into 18 families, in all totaling 986 known species in the world.  They inhabit most temperate and tropical regions of the globe and are one of the most numerous forms of mammals on the planet. Only rodents have more species than bats.  The most obvious and unique distinctive feature that bats have is the capability of flight. They are the only mammals who have this capability, which is granted to them by skin membranes that extend out from the side of their bodies and their tails to connect their limbs with their main bodies. The forearms and fingers have been adapted to support these membranes, with long extended fingers and slender bones. The entire body of the bat is designed for flight, with flattened ribs, an extremely well supported shoulder girdle and clavicle, and a rigid sternum.

Another highly unique characteristic of bats is their employment of echolocation for nocturnal orientation. Vocal sounds emitted through the nose or mouth by a bat in flight bounces off surrounding objects, effectively giving them a sensory system analogous to radar. This extra sense allows bats to avoid running into obstacles at night and to detect the position of flying insects or other potential food sources.

Bats generally tend to roost in a permanent shelter, consistently returning to the same place to rest. Shelters can include cages, trees, crevices, and even buildings. These relatively secure areas are where bats hibernate when conditions are unfavorable, such as a climactic change or reduction in food supply. During hibernation their body temperatures drop significantly, reflecting a marked decrease in metabolism and oxygen consumption. Temperatures and metabolism return to their normal states immediately following the reawakening of the bats.

A common method of characterizing bats is differentiating them by their distinct diets. Because of the overall species diversity of bats, these diets spread over a large range of food sources. Many can be characterized as follows:

        - Insectivorous:
                - most insect food obtained by flying
                - most will eat some fruit
                - largest and most diverse group of bats
        - Frugivorous:
                - feed almost exclusively on fruit
                - will eat some green vegetation
                - sometime work together in groups
                - live in tropical environments where fruit is 
                  constantly ripening
        - Nectivorous:
                - diet consists mainly of pollen and nectar
                - will eat some insects found in flowers
                - mainly tropic and subtropical bats
        - Carnivorous:
                - prey on frogs, birds, lizards, small mammals, other bats
                - extremely varied diet
        - Fish-eating:
                - catch fish near or at the water surface
        - Sanguivorous²:
                - feed off of blood (i.e. vampire bats)
                - original diet from peccaries, tapirs, and other large mammals;
                   introduction of cattle by farmers gave another target
                -  two species feed on bird blood

        All of the above types of bat can be found in the Amazon rainforest, making them an exceptionally good indicator species, since they are affected by multiple factors due to their reliance on a diverse amount of food resources. Due to the large biomass and abundance of life in the rainforest, the Amazon is an especially ideal environment for large colonies and an assorted number of bat species that can be monitored at all different levels of the canopy.

Amphibians
 

Why monitor amphibians?

Amphibians are set apart from other creatures by the fact that they absorb a great deal of chemicals through their skin as well as through the thin, moist linings of their mouth and throat.  This makes them especially sensitive to pollution present in the environment.  In addition to their wide distribution and large numbers throughout the rainforest, they make an ideal set of animals for the monitoring of toxin levels in the rainforest.  They also constitute a large enough food base for predators and a large enough controlling force for insects and other animals that any disruption in the population numbers of this group of animals is likely to cause upheaval in the Amazonian food web.

How will they be monitored in the Amazon?

Due to the extensive nature of the Amazon Rainforest and the limited budget and number of personnel involved with the project, monitoring will consist of what will be essentially "hot spot" checks.  These will consist of blood tests on randomly selected animals of at least two species³ in areas of concern to determine the exact degree to which the ecosystem is being polluted.  Additional tests, such as gross anatomical observations for deformities and chemical testing for behavioral abnormalities will be conducted to determine the non-lethal synergistic effects of the polluting chemicals on the amphibians^4,5.  "Areas of concern" will consist of areas of the rainforest where it is believed that pollution is, or could become a major problem for the overall ecosystem's health.  These include industrial waste dumping sites, farmland drainage areas (pesticide runoff), and any other site deemed threatened by pollution.  Monitoring actual population numbers will not be necessary unless the toxins present are severe enough in their effects to cause significant mortality rates.

Table 1: Miscellaneous Chemicals of Possible Importance to the Project (copper from mining, etc.)⁵

 

Parasites

Parasites are effective potential indicators of environmental quality due to the variety of ways in which they respond to anthropogenic pollution. Thus parasites provide valuable information about the chemical state of their environment through their presence / absence and ability to concentrate environmental toxins within their tissues. 

Specifically, parasites are useful in two different ways.  First of all, they are "effect indicators," that is they can reveal the effects of various pollutants on the abundance and distribution of fish.   However, because there is a wide variety of factors which affect the population of parasites, parasites do not allow any conclusions to be drawn concerning the concentration of specific toxins in the environment. 

One example of the use of parasites as an effect indicator is the Monogenean Trematode, which lives on the gills of fish. Because this parasite is in direct contact with both the surrounding environment and the host fish, it is a particularly good indicator species.  In addition, its short lifespan means that it immediately reacts to environmental changes.  Other effect indicator species include the Dreissena and Salmo gairdneri, which are hosted by zebra mussels and rainbow trout, respectively.  These species are good indicators of the quality of water treatment in sewage plants. Dactyloyrus and Paradiplozoon are also effective indicators of the concentration of effluent resulting from pulp and paper mills. 

Second, parasites can be used as "accumulation indicators"⁶. By looking at the concentration of environmental toxins within the parasites, we can monitor the environment.  This method takes advantage of the fact that parasites usually have higher concentrations of metals in their bodies than their host has in its tissues.  For example, the lead burden in the parasites is about 1000 times that of the host's muscle. This is because metal concentrations in parasites are likely to respond rapidly to changes in environmental changes. 

For example, the presence of acanthocephalans had a significant impact on lead accumulation in the intestinal wall. The fish infected with acanthocephalans has only half of uninfected chub's lead concentration. Acanthocephalans is a group of intestinal worms commonly found in fish. Adult worms live inside the intestine of the final host and absorb their nutrients across their tegument⁷. There are three major species: 1) Pomphorhyndchus laevis, 2) Acanthocephalus lucii, and 3) Paratenuisentis ambiguous. Among these, P. Laevis most rapidly reacts to changes in the environment. The mean concentrations of lead and cadmium in P. Laevis are respectively 2700, 400 times higher than in the muscle of the host and 11000, 27000 times higher than in water. Acanthocephalans can accumulate toxic metals from the aquatic environment to concentrations even surpassing those in Dreissena polymorpha⁸ (Sures, 2001).

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Bioindicator Foot Notes:

1: Medellin, Rodrigo A. (2000). "Bat Diversity and Abundance as Indicators of Disturbance in Neotropical Rain forests." Conservation Biology, 14(6), 1666-1675

Bats, Amphibians and Parasites Footnotes:

1: Order Chiroptera: Bats. John Hopkins University Press, 1997 
   <www.press.jhu.edu/books/walkers_mammals_of_the_world/chiroptera/chiroptera.html>

2: Organism of the Week: Bats. Wooster University, 1998
   <http://www.wooster.edu/biology/mloveless/OOWthisweek.html>

3: van Straalen, Nico M. (2002) Assessment of Soil Contamination - a functional
   perspective. Biodegeneration. 13: 41-52.

4: Cockell, Charles S.  Ecosystems, Evolution, and Ultraviolet Radiation.  Springer-Verlag.  c2001.
 

5: Devillers, J., and Exbrayat, J. M. Exotoxicity of Chemicals to Amphibians. Garden and Breach Science Publishers.  c1992.

6: Accumulation of toxins within parasites

7: Acanthocephalans do not have mouth nor intestine

8: Dreissena polymorpha is a kind of mussel. It is one of the best established accumulation indicators in fresh and brackish waters in Europe and USA.