The container flora fauna and environment

It is November in southern Ontario. An icy wind pierces clothing and trees and makes field work a chore to be hastened rather than the usual pleasure. We walk down to a boggy lakeside, ice crackling underfoot - making crossing a makeshift bridge more than usually difficult. On the lake itself the ice is spreading: not yet locking down the whole surface but forming a corona around the rim on which the black ducks stand disconsolately. The ground vegetation changes as we approach the lake: from leaf litter and the dried grass tussocks of winter, it becomes spongy sphagnum bog interspersed with a few dwarf pines. And it is deeply embedded in this sphagnum that Dolf Harmsen of Queen's University and I find what we are looking for. Just visible above the moss profile are the red and green leaves of Sarracenia pitcher plants: still half-filled with liquid and, even in the winter cold, with one or two larvae of the pitcher-plant mosquito, Wyeomyia smithii, swimming within them. The rest of the bog is biologically silent, only the wind in the pines breaking the heavy winter pall which hangs over the northland - at least to the eye and ear of an antipodean naturalist!

In contrast, I think of a village stand of bamboos just outside Madang in New Guinea. The air is hot and humid and filled with mosquitoes. The grove of bamboos is enormous and the stems themselves up to ten or even twenty centimetres across. This is a village resource held in common as a source of building material, scaffolding, piping, walking sticks, children's toys, and a hundred and one other uses. Each time the stand is cropped, the required stems are severed with the ubiquitous New Guinean 'bushknife' - as likely as not a wickedly sharp length of metal which began its life as the leaf of a car spring. Each cropping leaves a bamboo stump and, in consequence, a cup between the point of severence and the next nodal plate. In the perhumid climate these fill with water rapidly and are the home of a wide range of animals that feed either on the plant detritus which accumulates within the cups, or on each other. But this particular stand comes to mind because here too the ground is covered with the inflorescences of what is sometimes called native turmeric, Curcuma australasica These are spikes of relatively inconspicuous white flowers each enclosed with a fleshy pink bract, and each of these bracts too is water filled. The bract water of each of these inflorescences is alive with the tiny white larvae of the mosquito Uranotaenia diag-onalis and, occasionally, the voracious predatory larvae of the muscid fly Graphomya. The muscid larvae, unlike the mosquitoes on which they feed, are able to move freely from one bract axil to the next in order to keep up with the appetite that must be satisfied in order to complete the species' life cycle within the month or so that represents the life time of the inflorescence itself.

Subarctic bogs and New Guinean rainforest may seem to have little in common but, in each, I have sought and found plants that provided water-filled container habitats for a variety of animal species. And I could have painted, instead, word pictures of English deciduous forest, Indonesian lakesides, Bornean mountain tops or cool temperate Gondwanic rainforest in Tasmania: each of these and most other ecosystems present examples and opportunities to students of phytotelmata.

In the next three chapters I review the widely scattered and sometimes obscure literature on the plants in which phytotelmata form (Chapter 2), the range of metazoan animals which occur within them (Chapter 3), and the physical and chemical properties of the environments themselves (Chapter 4). By including a more extended account of the animals, family by family, in an Annexe at the end of the work, I have attempted to make the review as complete as possible and, in this Annexe and the associated references, I have deliberately set out to save future workers a massive amount of delving in the older and non-English literature involved. The literature up to mid-1997 has been covered although, inevitably, some items will have been missed. In particular I know I have only scratched the surface of the immense literature on mosquito biology.

The container flora The water-holding plants

Phytotelmata are formed whenever watertight hollows appear as part of the growth form of plants. They occur as five principal types with any number of additional minor categories. These five types - bromeliad 'tanks', pitcher plants, water-filled tree holes, bamboo internodes, and axil waters collected by leaves, bracts or petals - are all formed from parts of living plants. In a few instances water-collecting hollows are formed in the fallen parts of plants. For all these categories, in the vast majority of instances, the plants concerned are angiosperms. However, water-filled tree holes are recorded from a few 'lower' plants such as tree ferns and cycads, and Lounibos (1980) describes mosquito larvae from the rain-water pools collected in the concave tops of fungal basidiocarps.

In reviewing the plant groups from which an aquatic metazoan fauna has been recorded I draw heavily on the reviews of Thienemann (1934, 1954), Kitching (1971) and Fish (1983). Fish (1983) estimates that more than 1500 plant species may form phytotelmata. Given that water-filled tree holes may form, with greater or lesser frequency, in almost any species of tree, I suspect that this number is a significant underestimate.

I describe this special flora using the classification of phytotelmata alluded to above.

Bromeliad 'tanks'

According to Frank (1983) the Bromeliaceae contain about 2000 species of plants divided into three subfamilies and about 50 genera. All but one of these species occur in the warm temperate to tropical regions of the Americas, from Florida to central Argentina and Chile. The exception, Pitcairnia feliciana, occurs only in Guinea in West Africa. Bromeliads are herbaceous perennials which occur as terrestrial plants, although are better known as epiphytes in the rainforest canopy. Many species may co-occur and plant densities can reach very high levels. Although essentially an American group, the bromeli-ads have long been popular in horticulture in warmer parts of the world and undoubtedly act as breeding sites for aquatic organisms well outside the plants' natural range. Thienemann (1934), for example, recorded organisms from bromeliads growing in the Bogor botanic garden in his survey of container habitats in South-east Asia.

All so-called 'tank' bromeliads impound water in their leaf axils which overlap tightly to form watertight cavities. The outer, more mature leaves form discrete water bodies; the younger, inner leaf axils combine to form a common pool (Beutelspacher 1971, Zahl 1975, Frank 1983) (Figure 2.1). Species of bromeliad from the two more advanced subfamilies, the Tilland-sioideae and the Bromelioideae, have growth forms which may form such water-holding tanks (Pittendrigh 1948). Fish (1983) reports that about 40 of the 50 genera of bromeliads form water bodies of this kind.

The communities of animals which occur within bromeliads have been objects of fascination for many years, inspired originally perhaps by the extensive and detailed work of Picado (1913) who studied species of the Aech-mea, Billbergia, Guzmania, Tillandsia, Thecophyllum and Vriesia in Costa Rica. Picado recorded all of the animals he found in and around bromeliads from Protozoa to fer-de-lance!

Table 2.1 reviews the literature on the aquatic communities which live in bromeliads. In this and other tables in this chapter I have omitted simple fau-nistic references to the occurrence of particular organisms in various phy-totelmata. Some of these references are to be found in Chapter 3 dealing with phytotelm fauna: in other cases entry to the literature may be obtained through the more general ecological references reviewed here. In the case of the bromeliads, Frank (1983) provides an extensive set of such references. In general the literature on bromeliad communities comprises general, semi-popular accounts (e.g. Zahl 1975, Beutelspacher 1971) and accounts of studies of bromeliad-inhabiting mosquitoes, either as vectors of malaria (Downs & Pittendrigh 1946, Pittendrigh 1948 et seq.) or as nuisance pests (Frank & Curtis 1977 et seq.). Very few accounts deal with the community of organisms within the contained water bodies. Of these few that of Laessle (1961), dealing with the bromeliad genera Guzmania, Tillandsia and Hohenbergia in Jamaica, is outstanding and rivals Picado (1913) in completeness. The production of more complete accounts of the faunistics of bromeliad tanks allowing the construction of food webs for comparative analysis remains one of the major opportunities within phytotelm studies which was taken up, more recently, by Cotgreave et al. (1993).

Shoot Borer Large Cardamom
Table 2.1. Key works on the aquatic communities associated with the Bromeliaceae

Author(s)

Year(s)

Bromeliad genera or species

Subject matter

Beutelspacher

0 0

Post a comment