Keystone Plant Research Articles

Drought and the consequences of El Niño in Borneo: a case study of figs

AbstractBorneo has a perhumid climate but occasional severe droughts have an important impact. Droughts may affect the composition and size structure of plant communities through differential mortality or, via their impact on the availability of plant resources, affect plant–animal interactions. From January to April 1998, northern Borneo suffered a very severe drought linked to the El Niño Southern Oscillation event of 1997–1998. In this article, the impacts of this drought on the rain forest at Lambir Hills National Park, Sarawak, are considered with special reference to a keystone plant group, the figs. Small fires entered the edge of the forest from the roadside, killing saplings, climbers, and understory trees. Community‐wide mortality for adult trees was 0–7 times higher than in nondrought years, with larger trees showing a greater proportional increase. In figs, mortality was significantly higher in pioneers, but hemiepiphytes and roadside species were unaffected. Phenology was substantially affected. Leaf and flower/fruit production decreased or ceased during the drought and increased suddenly following renewed rain. Pollinators of dioecious figs became locally extinct during the drought, and other plant–animal interactions may also have been disrupted. The frequency and severity of droughts has increased substantially in the past three decades, and climate models suggest this may be the result of global warming. The impacts of the 1998 drought at Lambir Hills National Park suggest that, should this trend continue, a substantial alteration of habitats and overall loss of biodiversity can be expected in Borneo.

Identifying keystone plant resources in tropical forests: the case of gums from Parkia pods

Keystone plants that produce seasonally critical trophic resources comprise one of the main classes of keystone species, yet no studies have attempted to examine the ecological attributes that might help us recognize them and evaluate their importance in species-rich plant assemblages. In this paper the concept of keystone plant resources is reviewed using potential candidates proposed in the literature for neotropical forest sites. A poorly known example of a potential keystone resource—the gums produced by mature pods of two emergent tree species (Parkia nitida and P. pendula, Leguminosae: Mimosoideae)—is described for primates and other arboreal vertebrates in Amazonian forests. In particular, the fruiting phenology, tree density, patterns of vertebrate consumption, and nutritional quality of Parkia gums in Amazonian terra firme forests are considered. Putative neotropical keystone resources are then divided into four intersecting ecological attributes defining their community-wide importance to vertebrate frugivores: (1) temporal redundancy, (2) degree of consumer specificity, (3) reliability, and (4) abundance. From a vertebrate perspective, keystone plants are here defined as those producing reliable, low-redundancy resources that are consumed by a large proportion of the bird and mammal assemblage with which they coexist. Plant populations proposed to date as keystone species range widely across two of these four variables, which may disqualify most putative taxa (including Parkia spp.) from a more formal definition of keystone resources. Other importance attributes, the context-dependent role, the taxonomic refinement, and removal effects of the keystone plant resource concept as applied to tropical forests are also discussed.

The breeding structure of a tropical keystone plant resource

Despite the recognized importance of maintaining viable populations of keystone plant resources in tropical wildlife parks and forested preserves, the critical question of what constitutes effective breeding units of these species has not been directly addressed. Here we use paternity analysis techniques to reconstruct the genotypes of pollen donor trees and to estimate pollen dispersal distances and breeding population size parameters for Panamanian populations of seven species of monoecious strangler figs (Ficus, Moraceae), a particularly widespread and influential group of keystone producers1,2,3. Despite the minute size (1–2 mm) and short lifespan (2–3 d) of the species-specific wasp pollinators (Agaonidae, Chalcidoidea), pollen dispersal was estimated to occur routinely over distances of 5.8–14.2 km between widely spaced host trees. As a result of such extensive pollen movement, breeding units of figs comprise hundreds of intermating individuals distributed over areas of 106–632 km2, an order of magnitude larger than has been documented for any other plant species. Moreover, these results should be generalizable to the 350 or so monoecious fig species that share this pollination system4. The large areal extent of breeding units of these keystone plant resources has important implications for our understanding of both the evolution of tropical biodiversity and its maintenance by applied conservation efforts.

Reproductive and Genetic Consequences of Forest Fragmentation: Two Case Studies of Neotropical Canopy Trees

Large areas of continuous tropical forests are rapidly becoming fragmented as a result of human activities, prompting a growing need for information on the reproductive and genetic responses of tree species to disturbance. Here we review the literature on pollen dispersal in continuous forest stands in order to identify factors expected to enhance or to inhibit interfragment pollen flow. We then describe two empirical studies of the effects of fragmentation on pollen flow in Neotropical populations of Spondias mombin (Anacardiaceae) and five monoecious species of Ficus (Moraceae). In S. mombin, small fragment populations suffered significant reductions in germination rate and fruit production relative to large fragment and continuous forest populations. Nevertheless, 90-100% of the progeny produced in the small fragments were the product of pollen gene flow originating from forest stands located over 80-1000 m away. In contrast to S. mombin, which is relatively abundant and pollinated by a variety of small insects, the strangler fig species studied were relatively rare and pollinated by species-specific wasps that are both small and short-lived. Paternity analyses revealed these highly coevolved pollinators to be effective agents of pollen movement over very long distances, routinely dispersing 6-14 km to receptive host trees. Because of such extensive pollen flow, breeding populations of figs were estimated to consist of hundreds of intermating individuals distributed over 108-632 km2, an area substantially larger than has been documented for any other plant species. The observed patterns of dispersal in S. mombin and Ficus demonstrate the potential for ecologically and evolutionarily significant pollinator and pollen movement among populations occurring in both disturbed and continuous forest environments. Moreover, given the integral relationship of figs, as keystone plant resources, to other plant and animal species, the extensive spatial scale of fig breeding units demonstrates how the conservation of biodiversity in spatially isolated reserves may be dependent on the preservation of forest elements in a surrounding fragmented landscape.

Ficus─a keystone plant species in the tropical rain forest ecosystem of south Yunnan

Ficus─a keystone plant species in the tropical rain forest ecosystem of south Yunnan

Ingestion of Ficus enormis seeds by howler monkeys (Alouatta fusca) in Brazil: effects on seed germination

Figs (Ficus spp.) have been considered keystone resources for Neotropical frugivores. Such keystone plant resources are characterized by playing important roles in sustaining frugivores through periods of general food scarcity (Terborgh 1986). Many birds and mammals consume figs and disperse their seeds (e.g. Coates-Estrada & Estrada 1986). Howler monkeys (Alouatta spp., Cebidae) are important consumers of figs (Milton 1980). Although it has been accepted that frugivores allow the passage of fig seeds undamaged through their digestive tracts (Janzen 1979, but see Janzen 1981), few quantitative studies exist on the effect of dispersers upon the germination of fig seeds (Coates-Estrada & Estrada 1986, Midya & Brahmachary 1991, Utzurrum & Heideman 1991). Here I report the effect of brown howlers (Alouattafusca Geoffroy) on the germination success of Ficus enormis (Mart. ex Miq.) Miq. This fig species is a strangler tree reaching heights of approximately 15 m, and producing globe syconia (12.70 ?1.02 mm long, 12.82 ?1.19 mm wide, N = 30) which turn brown when mature. Field observations were conducted in the Reserva de Santa Genebra, a tropical upland semideciduous forest (Morellato 1991) in Campinas, Sdo Paulo (220 49' S 470 07' W) between April and June 1992. Ficus enormis fruits at this site are consumed mainly by Alouattafusca, Cebus apella, Artibeus lituratus, Sciurus ingrami (Galetti 1992), and the toucan Ramphastos toco Muller (pers. obs.). Primate faecal samples were collected from the forest leaf litter, mostly below one single fig tree. Seeds used in the germination tests were selected at random from the faeces defecated by a group of five howler monkeys. Seeds used in control germination trials were also randomly chosen from fruits dropped to the ground during primate feeding bouts in the fig crown. The seeds were sown on

Predation on palm nuts ( Syagrus romanzoffiana) by squirrels ( Sciurus ingrami) in south-east Brazil

Although Terborgh (1986) suggested that palm nuts are a 'keystone plant resource' for frugivore communities in tropical forests, few studies exist on seed ecology of palm fruit crop (Bradford & Smith 1977, Pifiero etal. 1984, Vandermeer et ali. 1979). Janzen (1983) suggested that seed predators have a major impact on the structure of plant communities in tropical forests. Squirrels are regarded as important seed dispersers and seed predators (Glanz et ail. 1982, Janzen 1972) depending on the habitat and the fruit availability. These rodents frequently consume hard nuts and their distribution may be related to the distribution of food sources such as palms (Glanz 1982). This paper investigates the utilization of the fruits of the 'geriva', ySyagrus romnanZoffiana (Cham.) Glassmnan by squirrels in a tropical upland semideciduous forest in south-east Brazil. Field observations were made from August 1988 to May 1990 in the 250 ha Santa Genebra Reserve in Campinas (22? 49' S, 470 07' W), Sao Paulo State, Brazil. The climate of the region is characterized by one dry (April to September) and one rainy (October to March) season; annual rainfall during the study period was 1366 mm. The feeding assemblage that utilizes Sjyagruis fruits in Santa Genebra is composed of squirrels Seiinrus ingrami Thomas, a small species about 34 cm in length (H. Bergallo, unpub.), capuchin monkeys Cebus apella Linne and brown howler monkeys Aloucattafiusca Ihering. &yagrus rotinanzofJiana is a common palmi in semideciduous forests in south-east Brazil (H. F. Leitao-Filho, pers. comm.). The fruit is an ovoid drupe 2.5 cm in diameter, with a soft exocarp and woody endocarp. Individuals of this species produce fruit all the year round, each plant producing two bunches at a timie.

Are Figs Always Keystone Resources for Tropical Frugivorous Vertebrates? A Test in Gabon

This paper evaluates the suggestion of Terborgh (1986) that figs constitute “keystone plant resources” for frugivorous mammals and birds in African rain forests as they appear to do in South America and Asia. From studies of the diets of monkeys and other mammals and birds in Gabon, we show that figs are infrequently eaten by most species, and are always eaten in small amounts. Figs in Gabon occur at very low densities and have unpredictable fruiting patterns and relatively low crown production. Thus, fig fruits are not staple foods and cannot sustain most populations of frugivorous species during periods of low fruit availability. In Gabon, monkeys and large birds depend on the fruit of two species of Myristicaceae and of one species of Annonaceae. These regularly bear ripe fruit during the lean period and are abundantly consumed. Figs occur in such distant patches that they are mainly fed on by wide—ranging animals such as large frugivorous bats.

Keystone‐Loening Spinning Experiments

THE spinning tests conducted at the Keystone plant were started in a frantic effort to find an easy cure‐all for flat spins, in the same manner that the alchemists of old tried vainly to find the philosopher's stone that would perform the transmutation of elements. It was only after all the prevalent theories on causes of flat spins were tested that a real intelligent investigation started.