Cape sugarbird WHY SUCCULENT FLOWERS SEJ by A. V. Milewski energy, water and nutrients which are The Field Guide to Trees of not retrieved by the plant, because the Southern Africa by Van Wyk & Van very purpose of fruit-pulp is to be Wyk (Struik 1997) shows the flowers removed from the plant once it is and fruits of trees and tall shrubs in ripe. The more resources the plant the south-western Cape. Of eighty spends on flowers, the less generous it species (excluding conifers) with is likely to be with fruit-pulp. Plants fleshy fruits eaten by birds, 91 % have may be generally faced with a choice small, dull flowers which easily of dispersing pollen or seeds, but not escape the notice of the human both, by avian flight. observer. Members of up to thirty-nine The division between bird-polli­ genera in twenty-five families conform nated and bird-sown plants is clear in in having fly-pollinated flowers and the south-western Cape, which has a bird-sown seeds in the south-western climate with winter rainfall and Cape. Eight percent (e.g. Glllysanthe­ summer drought similar to the maides, Grewia, Solanum) resemble lowers and fTllits vary greatly in Mediterranean Basin. Proteas charac­ many species of cultivated fruits size and how much food they teristic of this area produce large (e.g. apples, plums, raspberries) in Foffer polli nators. The smallest blooms pollinated by sunbirds and having colourful petals attracting flowers are dull greenish, and attract sugarbirds. Olives (Oleaceae) produce medium-size insects such as bees and pollinators no larger than small flies. succulent fruits conspicuous to beetles. The only species of tree or tall Large blooms usually produce enough mousebirds and bulbuls (lacking shrub in the south-western Cape that nectar to attract birds as pollinators. gizzards) and the rameron pigeon uses birds for pollination as well as Fruits vary in an inverse way to (which has a gizzard gentle on seeds, seed-dispersal is Halleria lucida. flowers. A generous succulent compared to seed-destroying doves However, the sunbirds that pollinate wrapping may be digested by birds, and pigeons). Although proteas lack the mainly red flowers of this honey­ rewarding them for passing the seeds petals, and spend energy on bulky suckle are not among the birds that intact for germination. This ripe fruit­ protection for their dry seeds, each usually eat its dark purple fruits. pulp may consist of up to 90% fruit­ bloom contains many flowers that do There are fifty-two species of trees juice. Alternatively, fruits may dry not produce seeds. For each seed and tall shrubs with dry fruits ignored and split with maturity, releasing dry produced, proteas devote more energy by most h'uit-eating birds in the south­ seeds. What is odd is that it is usually to nectar than to fruits. Seeds of western Cape. A few (e.g. Dadanaea, the large, generous flowers that certain species of Leucaspermum and Glutia) have the small, dull flowers produce the dry fruits, and the small Mimetes have a small food-body otherwise associated with succulent flowers, with negligible nectar, that attached like a handle, sufficient to h'uits, but most have colourful flowers produce the succulent fruits. reward ants for sowing the fallen (e.g. pink in Galadendrum), or small Birds are affected accordingly. seeds. HowiWer, this does not cost as whitish flowers massed together for Birds with syringe-shaped beaks suck much as the swee"t·or oily wrappings display (e.g. Buddleja, Brabejum, nectar while pollinating flowers, and on the seeds of e~. Rhus, Gymna­ Gunania). Blooms attractive to birds birds with relatively stout beaks sparia and Putterlickia. These are found in Proteaceae, Aloe, swallow fruits, extracting the juice in members of the Anacardiaceae and Burchellia, and Schatia in the south­ their stomachs before regurgitating or Celastraceae have small flowers, and western Cape, according to Van Wyk defaecating the whole seeds. What is are accordingly so~n by birds and Van Wyk. There are also more odd is that bird species specializing in although tlo1'eir frJits lose their than sixty local species of Erica not nectar usually do not take fruit-juice, succulence by drying out as they qualifying as tall shrubs, pollinated by and vice versa. This mutual exclu­ ripen, in the south-western Cape and sunbirds. Unlike many Ericaceae siveness between flowers and fruits, elsewhere under similar climates. found in the Mediterranean Basin'and expressed in both plants and birds, is Two types of plants often break the on other continents (e.g. blueberry), so common that it has virtually been rule that succulent flowers and these have dry fruits. overlooked by Science. succulent fruits tend to be mutually Many of the common species of Why do succulent flowers seldom exclusive. Various honeysuckles may bulbuls, starlings, and weavers of the produce succulent fruits, and why do produce copious nectar in tubular south-western Cape are capable of birds not accept nectar and fruit-juice flowers, followed by sweet, succulent sucking nectar and pollinating in combination? Perhaps the basic fruits. These fast-growing shrubs act flowers. Even the fruit-eating speckled reasons are that few plants can afford as pioneers, temporarily enjoying mousebird and rameron pigeon have to produce fruit-juice after producing access to resources sufficient for been observed taking nectar from nectaI' and large flowers, and nectar is plants larger than themselves. Aloe, without destroying the petals, not rewarding enough to attI'act birds Mistletoes (Loranthaceae) may elsewhere in South Africa. However, to carry items larger than pollen produce bird-pollinated flowers and most birds usually ignore nectar, and grains. red, succulent fruits. Because parasitic Plants pay birds to carry their plants suck juices from trees and propagules, by offering fuel, usually shrubs used as hosts, some mistletoes in the form of sugars. However, there are able to afford nectar as well as are extI'a costs. Petals are fragile, and paying small perching birds to sow the nutI'ients they contain may be sticky seeds on the stems of host wasted after serving their purpose of plants. Honeysuckles are represented display. Although not eaten by polli­ in the south-western Cape by HaIJeria nating birds, petals may be eaten by (Scrophulariaceae) and at least one other animals. Blooms do not sustain species of Lycium (Solanaceae). themselves by photosynthesis, Mistletoes in this area include because a green colour would hide Septulina glauco, which parasitizes them from biI'ds. Fruits contain Lycium. Seeds of Kiggeluriu ufricunu 80 Veld &' Flora June 2000 )M PRODUCE SUCCULENT FRUITS IN MY OPINION leave the patches of Proteaceae and certain fruits (e.g. Kiggelaria africana smallest of Australasian honeyeaters Erica to sunbirds and sugarbirds. Cape in the south-western Cape) contain (less than 10 g). South Africa alone whi te-eyes eat both nectar and fruit­ fats as well as sugars. The available contains certain vegetation types pulp, but they are too short-billed to payment of dilute energy can sustain dominated by bird-pollinated plants pollinate most flowers, and too small only relatively small body sizes, and (e.g. Pratea fynbos) and others to disperse most seeds. Instead, they plants do not encourage the eating of dominated by bird-sown plants (e.g. cheat on both types of plants, stealing petals needed for display. Fruit-eating thickets and forests of Olea). Since all nectar by pecking holes in floral tubes birds require extra protein rather than the vegetation of low trees or tall to avoid the anthers, and stealing energy, and are unlikely to be attracted shrubs here is dominated by either fruit-pulp by pecking holes into fruits to the meagre rewards offered by bird-pollinated or bird-sown plants, without swallowing seeds. Halleria plants for the transportation of pollen. it is remarkable that there are no lucida can be sown even by white­ Nectar-eating birds differ in shape equivalents for small hum.mingbirds, eyes because its fruit-pulp contains from fruit-eating birds, mainly because large honeyeaters, the Australian many small seeds. Even in the case of of their sizes. The beaks and tongues mistletoebird or the emu in the mistletoes in the south-western Cape, of sunbirds, sugarbirds, humming­ south-western Cape. the pollinators (sunbirds) differ from birds, and honeyeaters are not neces­ Unusually large ground orchids the seed-sowers (e.g. pied barbet). sarily longer than those of fruit-eating attract relatively large pollinators in Nectar-eating birds are everywhere birds but are effectively syringes fitted the south-western Cape. Most orchids smaller than fruit-eating birds, to small bodies. Bird-pollinated are particularly thrifty with their although size-ranges overlap. The sweet juices, perhaps because they largest pollinator (Cape sugarbird at photosynthesize relatively slowly, and 35 g) is less than one-tenth the body , The more resources the plant rely for energy partly on decomposing mass of the largest seed-sower in the spends on flowers, the less plant matter. Orchids tend to produce south-western Cape. Indeed, the little nectar, instead deceiving polli­ rameron pigeon is more massive than generous it is likely to be with nators by mimicry. These plants also any bird specializing in nectar, fruit-pulp. Plants may be produce aggregated pollen, which is including the relatively large generally faced with a choice deposited in a cohesive mass Australian honeyeaters. The Cape (pollinium) on visiting pollinators. sugarbird is nearly as large as the of dispersing pollen or seeds, Because their wind-borne seeds are Cape bulbul, but is much smaller than but not both, by avian flight., hardly larger than pollen grains, the speckled mousebird (50 g). The orchids are among the few plants in smallest nectar-eater (lesser double­ which pollen is effectively more collared sunbird at 8 g) is dwarfed by flowers assume tube shapes accord­ massive than seed.