The Skeptical Aquarist

Alternately, begin with a specific environment. The other way to organize your community is as an "ecotope," in which you recreate a very specific environment and populate it with two or three compatible species that characterize that environment.

Why do I want to call these "ecotopes" rather than "biotopes"?

"Biotope"--— literally "life-place"--— sets the actors against a setting. The "eco" of ecotope is the same element as in ecology, and also in economy; it derives in the end from the Greek word for household. Ecology studies the "household of nature," with all its interdependent organisms, whether they play dominant roles or minor ones. "Ecotope" reminds you that the biotic community aren't just passive residents in their environment, but they have a shaping effect on their local ecosystem, delivering CO2 or oxygen, reworking detritus, building humus, grazing patterns into algal mats, excavating nests and otherwise transforming it. The organisms can't be divorced from the setting. Biologists prefer the word "ecotope," which was coined by A. G. Tansley in 1936 to describe a natural unit of living and non-living components that interact to form a dynamic stable system.

"Ecotope" denotes an isolatable integrated ecological unit, consisting of a community of living organisms and their physical environment at a given time. Let me re-state that ecological definition of "community:" an association of bacterial, protist, plant and animal populations that are delimited by the particular area they live in and help to shape and maintain its characteristic physical attributes. You see that it describes an aquarium pretty well, too. The ecotope is a fine-scale system with a homogeneous character. It's smaller than a landscape or a watershed; it's the smallest isolatable unit. It's not your whole garden that's an ecotope; just the compost heap, or the fringe of unmown grass round the edge of the lawn, or even the place where you keep knocking out the ashes of your barbecue. An ecotope is a microhabitat. And because it's a microhabitat, you can make a stab at suggesting it, even in the restrictions of a glass tank. So a good choice for an ecotope aquarium will be specific and restricted.

In recreating your artificial ecotope, you can become unnecessarily doctrinaire. You might insist on a broad-leaved Echinodorus in your Orinoco rather than an Anubias that originated in the Congo basin. Or you could be more flexible in your plant choices. Gunther Sterba, in Aquarium Care (1967), pointed out in a brief section on the "biotope" aquarium that fish are in no way dependent on certain species of plants, as some insects are, but rather on certain plant shapes and leaf forms. It doesn't matter to the fish whether it shelters under a plant from Africa, Asia or the Neotropics; the important thing is the type of shelter provided. Similarly, species that spawn on leaves are tied only to certain leaf shapes. And unlike some butterflies, plant-eating fishes will feed on a whole range of plants.

Dr. Sterba's "biotope" suggestions never caught on the the U.S. It was Rainer Satwikowski's book, The Biotope Aquarium (1993), presenting eight different aquarium "biotopes" with lots of color photos, that first got a lot of North American fishkeepers thinking about recreating specific water environments. Fishkeepers still tend to use "biotope" here in the U.S.

No one has done as much as Ted Coletti to popularize the idea of biotope aquaria in his series of columns "Aquarium Geographic" for F.A.M.A.. His article "Introduction to the habitat tank," at Mark Burningham's site, breaks down habitats into some useful broad categories like rainforest, monsoon forest and savanna, which apply to tropical systems everywhere. "Badman's Tropical Fish" offers concrete suggestions for plants and fish to evoke the general character of South American and South-East Asian blackwaters or slow-flowing swamps.

There are also some suggestions for ecotope aquaria at www.biotope-aquariums.co.uk, a personal website offering maps that divide the world into broad regions. The site gives you lists of fish species and plants found within those regions. It could offer you some very broad beginning outlines, within which you may want to recreate a more focused and specific biotope. This new site presents three ecotope set-ups evoking South-East Asian waters: a ditch, a shallow wetland and a slow-flowing stream.

Universal characteristics. Though the species that compose the local biota are endemic to each part of the world, in general, the kinds of freshwater environments are similar throughout the tropics. Hillstreams, for example, have steep gradients, where rapids and torrents scour the gravel, and seasonal floods may wash out the finer substrate. Tropical hillstreams have many other common characteristics, wherever you find them. Plankton are few there. Temperatures are cool. Water is still moderately soft. But depending on the continent you're working in, the hillstream fishes might be Southeast Asian Homalopterids or South American Loricariids.

Seasonal flooding in tropical and subtropical climates that experience the strong alternations of wet and dry seasons are commonly characterized as "monsoons" only in the Indian Ocean and Asia, but similar climate conditions with a consistent "dry" season create a characteristic vegetation in West Africa and in the Neotropics too. In any of these strongly seasonal climates, streambeds tend to accumulate tangles of brush during the spates of floodwaters, tangles which may last through several annual cycles. Waterlogged brush provides essential cover for many kinds of fish in vegetation-free waters. "Monsoon"-type forests are deciduous; the canopy opens when leaves fall in the dry season, and for months at a time strong light penetrates to the streams. In contrast, "everwet" tropics tend to keep a dense leaf canopy all year; their dim forest streams support no plant growth; they don't flood annually but their streambeds accumulate a deep litter of tree leaves.

Other widespread freshwater habitat types could focus your general picture into a specific ecotope: river backwaters or shoreline pools where tree roots have eroded out of a red clay bank. Shallow tannic water over a white silicate sandbar. Lowland streams, perhaps with leaf-littered banks, perhaps with overhanging vegetation. Has the scouring action of water in a standing riffle exposed buried cobbles? Or woody roots? Dim forest pools. More lightly-shaded pools in savanna grasslands. Are the grasslands flooded at high-water seasons, like the Brazilian/Bolivian pantanal? Or instead is it forest that's annually flooded, such as an Amazonian varzea? Clearwater streams, blackwater, of course; but would you dare recreate a whitewater ecotope with catlitter lateritic clay for mormyrids? Oxbow lakes. Blackwater lakes. Openwater ponds or waterlily-covered pools. Seasonally flooded riverside grass meadows of the Neotropics, or the manmade Asian watermeadows made for growing the grass that is rice. Reedbeds. Swamps. Peat bogs. Or coastal peat forest, such as the east coast of Sumatra has been? A weed-choked drainage ditch in Burma or its equivalent in Thailand? Subterranean limestone caverns offer unique environments, usually with endemic fishes.

If your "ecotope" aquarium is evoking a small pool or stream, you'll especially want to limit the number of fish species. "Upland forest streams and tributary headwaters exhibit a low alpha yet high beta diversity," says Prof. James Albert, U. of Florida. "This means relatively few species inhabit each locality, but there is a large turnover in species composition between localities. The opposite pattern is observed on the floodplains, where many species co-exist and each species has a more extensive range."

One characteristic of an ecotope is that it's unlikely to contain populations of two very similar species. But the temptation to assemble a Noah's Ark is hard to overcome: I've just been reading about a piranha "biotope" described at a website-- but it had three different species of piranha in it. In fact an ecotope is unlikely to have even two quite different species, if their living requirements are very similar.

The more specific the character of your ecotope, the more interesting it will be. Algae-covered rocky rubble at the base of a boulder near the shore of Lake Malawi sets a maybe-too-familiar stage for Malawi's mbuna cichlids. But the specific mix of species and morphs will be different from one bay to the next. Less familiar are the "snail graveyards" of Lake Tanganyika, where the coarse sandy bottom is densely littered with the shells of Neuthauma snails that make homes for dwarf Neolamprologus. The surface of the water is more important in an ecotope for Archerfish, which live in a tangle of mangrove roots in brackish coastal environments.

Often in an ecotope conception it's the edge habitat that's most interesting: the edge of a dense tangle of a single species of Cryptocoryne meets the clear area where the current is too strong for plants, in a Malayan forest stream.

Photos of characteristic ecotopes are sprinkled through many hobby-oriented books, even the Baensch Atlas. Look them over in detail for ideas. You'll find some beautifully recreated ecotopes in many of the modern public aquaria, though none of them seem to be illustrated and described on the Web. So far it's the familiar parade of orcas, sharks and tropical reefs.

Even if you don't read German, you'll find lots of evocative photos of tropical freshwater ecotopes that might inspire you at the sophisticated German aquarium e-magazine Aquaristik Actuell Jan 1996 to June 1997.

Good ecotope aquarium planning may take some ingenuity. See how one aquarist arranged a fast-flowing stream over cobbles, perfect for hillstream loaches, in the article "A river runs through it" at Loaches on Line.