Whatever the water storage form, it helps protect bromeliads from the worst rigours of dry spells between the intermittent rainfalls of their habitats, either arboreal or terrestrial. Indeed, some larger species are recorded as holding up to twenty litres of water after rain events. Yet there is far more to this than an easier existence for bromeliads because their water trapping habits have enormous impacts upon entire ecosystems especially arboreal ones, the prime focus of these notes. For example, one study in an admittedly sodden Colombian cloud forest estimated that bromeliads impounded over 50,000 litres of water per hectare. (Fish 1983 cited by Benzing1990.) Indeed, phytotelm bromeliads are so successful, so enormously varied, so numerous and widespread throughout the tropical forests (and beyond) of the Americas that large numbers of animal species are partly to totally dependent upon them for their very survival. Other, perhaps not so immediately obvious ecological benefits are increases in canopy humidity levels and a large increase of surface living areas in tree crowns that provide enormously more habitat niches. A very ecologically important example is that without epiphytes, bare tree branches would have few to zero nesting sites for ant colonies. (Benzing 1990.) This is hint number one.
Transient phytotelm users such as monkeys, snakes or lizards may want only a passing drink or snack but many frog and salamander species are dependent upon bromeliad phytotelmata for breeding and perhaps surprisingly, so are certain crab species such as the aptly named Bromeliad Crab Metopaulias depressus in Jamaican rainforests. (Diesel et al. 1993.) Insect species, especially aquatic juveniles; centipedes, millipedes, spiders and many other arthropods, even a few scorpion species; plus snails, worms, nematodes and numerous other creatures including weird but fascinatingly cute peripatus species add to an enormous list of bromeliad-living animals. Microbial and other life forms such as algae, bacteria, fungi and even parasitic plants add immensely more. (Frank et al. 2009.) There are probably more bromeliad users than there are of the nearly 3.000 currently known bromeliad species.
This outline of animal inhabitants shows that not all closely associated life forms are aquatic because older, humus-filling, hence increasingly drier outer leaf-gaps, especially in higher horizons of canopy soil accumulations provide a series of habitats for ever more dehydration resistant life forms that even include ant colonies. Hint number two. Incidentally, bromeliad phytotelmata are termed aquaria, while humus filled, outer leaf gaps are called terraria by biologists and humus accumulations in forest canopies are termed canopy soils by biologists. It is not at all surprising that phytotelm bromeliads have been described as “complex ecological microcosms” by the distinguished canopy researchers Lowman & Parker (2004.) Continual spatially close relationships of life forms are classed as symbiotic which essentially means two (or more) species living together and where such a relationship is beneficial to all parties involved, it is defined as being a mutualistic symbiosis. Phytotelm bromeliads also impound fallen organics, flow-through (dripping) nutrient-containing leachates both plant and animal derived and predator species bring in organics from beyond their adopted homes. The waste products of all occupying life forms help to contribute to the nutrient acquisitions of phytotelm bromeliads as impounded organics are catabolised (broken down) to simpler molecules with the help of resident detrivores (humus feeders) both ‘terrestrial’ and aquatic, so that end-product nutrients may be extracted by home plants.
Therefore, these relationships form a highly complex web of generalised symbiotic mutualisms. They are considered to be generalised mutualisms because resident life forms are seldom if ever restricted to any one bromeliad species.
Most arboreal but not all bromeliad species have tiny structures called trichomes that often densely cover their leaf surfaces. One could write entire books about leaf trichomes because they are so immensely varied in the plant world but suffice to say that bromeliad trichomes very probably make their leaves among the most efficient nutrient and moisture gathering foliages in the entire plant world. Certainly, bromeliad trichomes play vital roles in the uptake of nutrients from the “ecological microcosms” of phytotelm as well as in other bromeliad morphologies (forms) we have yet to explore. Nonetheless, I am not aware of studies that compare the nutrient uptakes of bromeliad leaves with those of carnivorous plants such as Drosera, Nepenthes or Pinguicula. Yet as we will see, certain Brocchinia species show some extremely interesting and informative comparisons. Also, take note for future considerations that the leaves of carnivorous plants do not extract nutrients from the atmosphere, certainly not in any significant manner.
We often think of phytotelm bromeliads as living in rainforests with continually closed canopies and certainly it is in these much more epiphyte-congenial habitats where most species thrive; however, some also occur in regions that annually experience much drier weather approximating the cooler seasons. Arboreal habitats without yearlong leafy canopies are not as able to provide steady supplies of falling organics and other important environmental benefits to epiphytes such as higher humidity and shade from overly intense insolation levels. Indeed, and I quote. “Growing conditions in canopies that epiphytes inhabit range from relative permissiveness to intolerable for higher plants”. (Lowman & Parker 2004.)
It is in open savannahs, seasonally-harsher deciduous forests and increasingly “intolerable” sites for epiphytes where we find evermore arboreal bromeliad species that do not have an ability to store rainfall in aquaria. For example, a study of bromeliads in a seasonally dry Mexican forest found that phytotelm bromeliads constitute only one fifth of local populations with air-plant bromeliads making up the remaining four fifths. (Reyes-Garcia et al. 2007.) The rainy season in some Mexican forests may only last for approximately two months each year but many more months of fogs and overnight dews assist plant survivals. In such environments, tank bromeliads are at a disadvantage.
My next instalment will explore some particularly interesting species within a popular group of arboreal bromeliads that do not keep aquaria.
Benzing, D. 1990. Vascular Epiphytes: General Biology and Related Biota. (Cambridge Tropical Biology Series.) Cambridge University Press.
Diesel, R. Schuh, M. 1993. Maternal care in the bromeliad crab Metopaulias depressus (Decapoda): maintaining oxygen, pH and calcium levels optimal for the larvae. Behavioural Ecology and Sociobiology. Vol. 32, (1.) pp11-15.
Frank, J. H. Lounibos, L P. 2009. Insects and allies associated with bromeliads: a review. Terr Arthropod Rev. 2009: 2: pp.125-153.
Lowman, M. Parker, B. 2004. Forest Canopies. Academic Press.
Reyes-García, C. Griffiths, H. Rincón, E. Huante, P. 2007. Niche Differentiation in Tank and Atmospheric Epiphytic Bromeliads of a Seasonally Dry Forest. Biotropica Vol. 40 (2.) pp168-175.
Plate 1. A dissected plant of the spiny northern form of Myrmecodia beccarii
showing the ant’s entrance passage at the plant base and the completely plant-grown complex of narrower ant-debris tunnels and lighter brown nesting cavities. Photograph by Attila Kapitany. http://www.australiansucculents.com/
Plate 2. A dissected tuber of the spineless southern form of Myrmecodia beccarii
showing a number of ant entrances at the plant’s base and the completely plant-grown complex of narrower ant-debris tunnels and larger lighter-brown nesting cavities. Photograph by Attila Kapitany. http://www.australiansucculents.com/
Plate 3. Part of a magnificent colony of the myrmecophyte Myrmecodia platytyrea ssp. antoinii
growing near the Lockhart River, Cape York Peninsula, North Queensland, Australia. Photograph by author.
Plate 4. A compact colony of young Myrmecodia beccarii “northern form”
with the species frequent ‘companion’ the so-called Button Orchid vine Dischidia nummularia growing in a mangrove swamp near Cairns. Dischidia nummularia is a parasite of the mutualism between the ant Philidris cordata and all Australian arboreal ant-plant species. Photograph by author.
Plate 5. The ant-plant Dischidia major
with mostly hollow ant-house leaves. Only a few ‘normal’ laminate leaves may be seen at centre because these are always the first to be lost in dry periods showing which ones are most important for survival. Iron Range National Park, Cape York Peninsula, North Queensland, Australia. Photograph by author.
Plate 6. Myrmecodia beccarii “southern form”
growing on a Paperbark Tree Melaleuca sp. in the swamps on the Hinchinbrook Channel. North Queensland, Australia. Sadly these forests would have been set back decades if not destroyed by the category five, cyclone Yasi in 2011. Photograph by author.
Plate 7. The weird but rare Australian myrmecophyte fern Lecanopteris sinuosa
at Elliott Creek, Cape York Peninsula, Queensland, Australia. Where it grows with fellow ant-plants Dischidia major, Hydnophytum moselyanum, and Myrmecodia platytyrea ssp. antoinii in riverine scrub on very nutrient poor silica sand soils. Photograph by author.
Plate 8. Jamaican bromeliad crab, Metopaulias depressus,
male. Barbecue Bottom, Jamaica. This species is arboreal, and lives and breeds in bromeliads. It has thus completely severed its ties to saltwater. www.kingsnake.com . Google stock images.