Bromeliad Dwellers

[i]Bromeliad Dwellers

Epiphytic bromeliads play a crucial role in the neotropical forest canopy. In what would otherwise be a dry environment, tank bromeliads impound fresh water, creating pools called phytotelmata, and their roots and leaves accumulate organic material creating soil far above the ground. Fish (1983, cited in Benzing 2000) estimated 50,000 liters of water were suspended per hectare in a Columbian cloud forest, and Paoletti et al. (1991) estimated the amount of suspended soil to exceed 100 kg per hectare in a Venezuelan cloud forest.

These arboreal systems have been likened to swamps where diversity is high and organisms are densely concentrated. In dry regions, terrestrial bromeliad tanks play an equally important role, since they may be the sole source of water for the local biota. For these reasons, bromeliads are considered to be keystone species, species that attract or harbor many other species and are essential for maintaining biological diversity.



In order to appreciate this diversity of bromeliad-associated organisms, a database is being developed that will eventually include all organisms reported to dwell in or on bromeliads or rely heavily on bromeliads for sustenance, shelter or courtship. The database can be accessed through the Florida Council of Bromeliad Societies web page at> www.fcbs.org/, clicking on the database button to the left and then "Bromeliad Tank Dwellers Database." It now contains more than 3300 reports from 42 countries, garnered from nearly 200 published references dating from 1878.
Bromeliad hosts have been identified in 107 species in 23 genera, but many (38%) of the citations do not include host taxon names, so the bromeliad diversity may be actually much higher. The most commonly reported host species are members of Tillandsia, not surprising given that Tillandsia is geographically widespread and highly diverse. Also well represented are Aechmea and Vriesea, again widespread and diverse.

Taxon names for both the host and the associated organisms are reported in the database as they appeared in the cited publication. However, in order to provide a consistent taxonomic scheme for sorting and searching the database, phylum, class and order names were added or changed to reflect a single, current concept. For the most part, the scheme of Barnes (1998) was adopted, especially for protists and animals. A few long recognized terms, like Insecta and Arachnida, were retained in the database, even though they are not used in the scheme of Barnes, because most users of the database are more familiar with them than the alternative terms.
Organisms belonging to each of the five kingdoms have been recorded from bromeliads. Relative representation in the database does not necessarily reflect the relative abundance of the different taxonomic groups in bromeliads, but rather the interests of the investigators.



The largest organism associated with bromeliads, and the only mammal in the database is the spectacled bear, Tremarctos ornatus (Peyton 1980). Members of Bromeliaceae make up the most important food source for this bear, which consumes fruits or the succulent rosette hearts of at least 22 species in the genera Puya, Tillandsia and Pitcairnia throughout its range in Peru. Bromeliads may be valuable sources of water to the bears, important in the scrub desert and steppe habitats where the bears live (Peyton 1980).

A number of birds also use bromeliads for feeding. Many bird species have been documented to forage in bromeliads, but Pseudocolaptes lawrencii (buffy tuftedcheek ovenbird) was the most specific feeder found, spending three-quarters of its time foraging in epiphytic bromeliads (Sillet et al. 1997). It consumed adult insects and arachnids but not aquatic insect larvae. The banaquit (Coereba flaveola) also uses bromeliads, but in this case it forages in the flowers for nectar. Although considered a nectar robber, it may play a role in pollination of the flowers. Of course, most bromeliads are pollinated by hummingbirds; and though clearly associated with bromeliads, hummingbirds have not been included in this database.

By far the most abundant chordates recorded in bromeliads are the Amphibia, including both frogs and salamanders. Because they require water for their eggs and juveniles, amphibians are often dependant on the water stored in bromeliad tanks. The small volume of water available in bromeliad leaf axils has led to some interesting adaptations in frogs, including small clutch size, elongate shape of the tadpoles and rapid development. As well as limiting the number of tadpoles that will grow in each small reservoir, small clutch size allows for more exposure of each egg to oxygen, important in the oxygen-depleated tank environment. To provide nourishment for tadpoles in food-limited phytotelmata some frogs provide unfertilized eggs for tadpoles to feed on; others invest in yolk-rich eggs, so that the juveniles needn't feed at all (Lannoo et al. 1987).



Some frogs are particular about which bromeliad they select: Osteopilus brunneus was found only in Hohenbergia fawcettii and never in Guzmania fawcettii, though both of these large-sized plants formed large arboreal clusters in the study area. This preference, does not hold throughout the frogs' range, since H. fawcetti is not present in much of the range. Other frogs are much less particular, and may utilize a variety of bromeliads or even artifical bromeliads provided by investigators (e.g. Syncope antenori; Krugel & Richter 1995).

As with frogs, adaptation to the leaf-axil habitat has had a profound effect on the only crab that breeds there, Metopaulias depressus (Diesel 1989, 1992). The ancestral home of crabs is marine, and most crabs still live there. Larvae hatch from eggs and simply float with the plankton for several weeks before developing into adult-like forms. In freshwater and terrestrial environements mother crabs may invest significant energies into care of their young, and the larval stage is either absent or greatly shortened. For Metopaulias depressus, mothering begins before the eggs are laid, when she cleans selected leaf axils by removing litter and any competitors for the space. Then, for the next four months, she stands guard over he eggs, larvae, and juveniles, bringing them food and chasing away predators, behavior completely unknown to other crabs (Diesel 1992).

Arthropods constitute the bulk of the tank-dwellers database, making up over two-thirds of all records, and insects alone comprise over half of the entries. Not suprising to those familiar with bromeliads, Diptera (the order that includes flies and mosquitoes) are most commonly reported.

The relationship of mosquitoes to bromeliad tanks has been of significant economic concern, because of the role of mosquitoes as vectors of human disease. The second most commonly reported insect order are the beetles (Coleoptera), the most diverse of all animal groups.



Other bromeliad-associated arthropods include arachnids (spiders, mites, scorpions, pseudoscorpions and harvestmen) and myriapods (millipedes and centipedes). Spiders are the most commonly reported arachnids. Lucus (1975) found that spiders outnumbered all other animals in Catopsis hahnii, and Oliveria et al. (1994) found spiders to be the most abundant animals in Neoregelia cruenta. Spiders are predators and may use bromeliads primarily for hunting, but one tarantula, Pachistopelma rufonigrum, has never been found outside of tank bromeliads. Like spiders, centipedes are predators, probably attracted to bromeliads for the other animals, but millipedes are predominantly herbivorous, feeding on the decaying vegetation that accumulates in leaf axils.

The kingdom with the lowest representation in the database is Plantae. The majority of records are the bryophytes, both mosses and liverworts. The liverwort genus Bromeliophila is found exclusively in bromeliad tanks, as its name implies. There are only two records of flowering plants in bromeliads. Seeds and seedlings of Erythroxylum ovalifolium, a close relative of coca, have been seen in Neroregelia crunenta (Fialho & Furtado 1993), the seeds presumably left by birds or tree frogs. The other flowering plant is Utricularia reniformis (Hoehne 1951), commonly known as bladderwort, a small plant that traps and digests insects in underwater, bladder-like sacs.



No doubt one reason for the poor representation of plants in the database is the prevalence of zoologists among bromeliad tank researchers. However, it must also be due in part to the low light conditions where bromeliads often grow. Laessle (1961) and Frank (1983) noted that algae are uncommon in shaded bromeliads because light levels are insufficient for photosynthesis to occur, and this must hold true for plants as well. In these conditions the food web is based on carbon from detritus (decaying plant and animal remains) rather than from photosynthesis. Animals play an important role in breaking detritus into small pieces, and thereby increasing its surface area, but the real work of decomposition and nutrient cycling is performed by microscopic members of the phytotelm community: bacteria, fungi and protists.

Only a single study has looked specifically for bacteria (and then only for coliforms; Hagler et al. 1993) present in bromeliad tanks, and only three studies included cyanobacteria ("blue-green algae") in their inventories, though bacteria may in fact be the most abundant organisms in bromeliad tanks as they are elsewhere. Tank water-associated fungi have been investigated only twice (Araujo 1998, Hagler et al. 1993) revealing numerous ascomycetous yeasts and a few Basidiomycota, also yeast-like. The majority of these fungi have been previously found in association with rainforest trees. Aquatic fungi are abundant in stream and lake systems, and may be present in bromeliad tanks, but have not been looked for yet.

A single investigation of bromeliad insect-associated Trichomycetes (Zygomycota) yielded a number of new species (Lichtwardt 1994), suggesting that futher investigation could not only expand the diversity of bromeliad organisms, but of fungi as well.



Protists have received slightly more attention than bacteria or fungi. The presence of green algae is associated with increased light, but the abundance of other, non-photosynthesizing protists (flagellates and ciliates) appears to be positively correlated with densities of rotifers and macroinvertebrates (Carrias et al. 2001). The same study found that flagellates and ciliates were present in tank waters at approximately the same densities as in fresh water systems. Thus, they are doubt important consumers of bacteria in bromeliad tanks and probably contribute more significantly to nutrient remineralization than do animals (Carrias et al. 2001).

Much work still needs to be done to inventory all organisms, especially microscopic ones, in bromeliad tanks. Above and beyond that, the ecological studies neccessary to understand the interactions of those organisms and the flow of energy and nutrients through phytotelm systems have not begun. We can all appreciate that bromeliads are extremely important contributors to biological diversity in neotropical regions, and a greater understanding of how bromeliad tank ecosystems function will further heighten our appreciation.



Literature Cited

Araujo, F.V. 1998
Notes on yeast communities of
bromeliad-tank waters of
Rio de Janerio, Brazil

Barnes, R.S.K. (ed) 1998 The Diversity
of Living Organisms. Blackwell
Oxford, UK.

Benzing, D.H. 2000 Bromeliaceae:
profile of adaptive radiation.
Cambridge University Press, Cambridge, UK

Diesel, R. 1989 (Decapoda: Grapsidae)
Parental care in an unusual environement;
a crab that lives in epiphytic bromeliads.

Frank, J.H. 1983 Bromeliad Phytotelmata;
Terrestrial plants as hosts for aquatic
insect communities.

Frank, J.H. and G.A. Curtis. 1981
On the bionomics of bromeliad-inhabiting
mosquitoes; Journal of the Florida Anti-
Mosquito Association.

Krugel, P. and S. Richter. 1995. Syncope antenori-
A Bromeliad breeding frog with non-feeding
tadpoles. (Anura, Microhylidae). Copeia 4:

JacksFloridaBromeliads

I really wish the pics were still up.