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Natural history, seed predation, and germination of Prosopis juliflora relative to a reforestation project in southwestern Ecuador
Abstract
Prosopis juliflora was studied in southwestern Ecuador for three months in conjunction with a reforestation project. Morphology and general natural history specific to this site is presented. In an effort to streamline the reforestation practices, seed predator insects and their interaction with germination was studied. When cleaned (septum removed), and uninfested and unaborted seeds were treated with hot water, 77% germinated within one week. Alternatively, seeds that contained a septum, and included infested and aborted seeds, under the same treatment yielded 12% germination over 8 weeks. The loss of seeds due to predation and abortion was 41% of the total. Sowing septed seeds caused an additional loss of 61% (of those left). Alternative processing methods and future recommendations for the planting of Prosopis juliflora are suggested.
... data, 1998). Flowers, buds and unripe fruits suffer predation by arthropods, with the larvae of specialist Bruchidae beetles affecting a large proportion of the seed production Agrawal 1996;Lerner & Peinetti 1996), and by birds including the parrots Cyanoliseus patagonus and Myopsitta monacha (pers. obs., 2001) and some passerines such as Phytotoma rutila and Poospiza torquata (J. ...
... None of the opened pod segments had the seed inside. We also recorded the number of closed pod segments with most or all of the fleshy mesocarp attached (Fig. 1a) and the number of closed pod segments with an emergence hole of an adult bruchid, usually used as an indicator that the seed has been predated during the larval stage (Solbrig & Cantino 1975;Kingsolver et al. 1977;Agrawal 1996). All the closed pod segments were then opened with pliers and the number of 'apparently viable' or 'sound' seeds (those that did not crumble when probed), the number of developed seeds that, even when not predated, were clearly not viable, and the number of empty pods (the seed was not developed, it had aborted or had been attacked, presumably by bruchids) were counted, per nest and sampling period. ...
... Recognition of this kind of dispersal (dyszoochory) challenges the usual assumption that a seed removed by a seed predator is a predated seed (Hughes & Westoby 1992;Levey & Byrne 1993;Beattie & Hughes 2002;Hulme 2002), even though it would also be wrong to consider it effective dispersal. For example, rodents may be able to find and prey on concentrated fruits left around nests or in trails, and the percentage of germination of enclosed Prosopis seeds is low (Solbrig & Cantino 1975;Agrawal 1996;Lerner & Peinetti 1996). Predation and dispersal may even be irrelevant factors acting on 'condemned' plants (Herrera et al. 1994;Maron & Simms 1997) due to unpredictable or ephemeral rains limiting germination, establishment and survival, or because of deleterious effects on seedlings related to the presence of the ant nest (Zavala-Hurtado et al. 2000). ...
Ants generally disperse seeds while feeding on fruits or structures attached to the seed. Seed dispersal as a by-product of seed predation (dyszoochory) was recognized in specialized harvester ants, but not in ants predating seeds opportunistically. Leafcutting ants are the main herbivores in much of the Neotropics, and they have been reported to remove fruits and seeds, but their role as seed predators and dispersers has not been acknowledged. Prosopis flexuosa D.C. (Fabaceae, Mimosoideae) is the most abundant tree species in the central Monte Desert, Argentina, and it is likely to depend on secondary animal dispersal. Mammalian frugivores are usually considered its main dispersers, but the opportunity for dispersal may be small since the removal of fruits and seeds by seed predators is very intense. The objective of this study was to identify which ant species interact with P. flexuosa fruits and to evaluate their relative importance as seed predators and dispersers. In a field experiment, whole and segmented pods were offered and several ant species exploiting the fruits were identified. Additionally, all pod segments remaining around nests of the three ant species able to remove them (the leafcutters Acromyrmex lobicornis Emery and Acromyrmex striatus Roger, and Pheidole bergi Mayr) were examined during and after the P. flexuosa primary dispersal season. Up to 753 pod segments and 90 sound seeds were found accumulated in a circle of 1 m radius over nests of A. lobicornis, and even more in an examined trail. Acromyrmex striatus left a smaller proportion of sound seeds and P. bergi left a smaller number of pod segments. All tendencies were similar during shorter known periods of accumulation. Leafcutting ants are acting as important seed predators, and ‘by mistake’ may be dispersing a key non-myrmecochorous tree. This is an unexplored path in the seed dispersal cycle of P. flexuosa that challenges the tendency to predict interactions based on classifications made with other goals.
... Regarding seed predation, there is convincing evidence of a high predispersal impact of bruchids, which can decrease Prosopis seed production by 25-70% (Smith & Ueckert 1974;Solbrig & Cantino 1975;Kingsolver et al . 1977;Agrawal 1996). On the other hand, the impact of postdispersal predators on Prosopis seeds is largely unknown. ...
... Regarding seed predation , there is convincing evidence of a high predispersal impact of bruchids, which can decrease Prosopis seed production by 25–70% (Smith & Ueckert 1974; Solbrig & Cantino 1975; Kingsolver et al . 1977; Agrawal 1996 ). On the other hand, the impact of postdispersal predators on Prosopis seeds is largely unknown. ...
Abstract The fate of seeds during secondary dispersal is largely unknown for most species in most ecosystems. This paper deals with sources of seed output of Prosopis flexuosa D.C. (Fabaceae, Mimosoideae) from the surface soil seed-bank. Prosopis flexuosa is the main tree species in the central Monte Desert, Argentina. In spite of occasional high fruit production, P. flexuosa seeds are not usually found in the soil, suggesting that this species does not form a persistent soil seed-bank. The magnitude of removal by animals and germination of P. flexuosa seeds was experimentally analysed during the first stage of secondary dispersal (early autumn). The proportion of seeds removed by granivores was assessed by offering different types of diaspores: free seeds, seeds inside intact endocarps, pod segments consisting of 2–3 seeds, and seeds from faeces of one herbivorous hystricognath rodent, the mara (Dolichotis patagonum). The proportion of seeds lost through germination was measured for seeds inside intact endocarps, seeds inside artificially broken endocarps, and free seeds. Removal by ants and mammals is the main factor limiting the formation of a persistent soil seed-bank of P. flexuosa: >90% of the offered seeds were removed within 24 h of exposure to granivores in three of four treatments. Seeds from the faeces of maras, on the other hand, were less vulnerable to granivory than were other types of diaspores. These results suggest that herbivory might be an indirect mechanism promoting seed longevity in the soil (and likely germination) by discouraging granivore attack. On the other hand, germination did not seem to have an important postdispersal impact on the persistence of P. flexuosa seeds in the soil. Both direct and indirect interactions between vertebrate herbivores and plants may foster P. flexuosa's seed germination in some South American arid zones.
... Regarding seed predation, there is convincing evidence of a high predispersal impact of bruchids, which can decrease Prosopis seed production by 25-70% (Smith & Ueckert 1974;Solbrig & Cantino 1975;Kingsolver et al . 1977;Agrawal 1996). On the other hand, the impact of postdispersal predators on Prosopis seeds is largely unknown. ...
The fate of seeds during secondary dispersal is largely unknown for most species in most ecosystems. This paper deals with sources of seed output of Prosopis flexuosa D.C. (Fabaceae, Mimosoideae) from the surface soil seed-bank. Prosopis flexuosa is the main tree species in the central Monte Desert, Argentina. In spite of occasional high fruit production, P. flexuosa seeds are not usually found in the soil, suggesting that this species does not form a persistent soil seed-bank. The magnitude of removal by animals and germination of P. flexuosa seeds was experimentally analysed during the first stage of secondary dispersal (early autumn). The proportion of seeds removed by granivores was assessed by offering different types of diaspores: free seeds, seeds inside intact endocarps, pod segments consisting of 2--3 seeds, and seeds from faeces of one herbivorous hystricognath rodent, the mara (Dolichotis patagonum). The proportion of seeds lost through germination was measured for seeds inside intact endocarps, seeds inside artificially broken endocarps, and free seeds. Removal by ants and mammals is the main factor limiting the formation of a persistent soil seed-bank of P. flexuosa: >90% of the offered seeds were removed within 24 h of exposure to granivores in three of four treatments. Seeds from the faeces of maras, on the other hand, were less vulnerable to granivory than were other types of diaspores. These results suggest that herbivory might be an indirect mechanism promoting seed longevity in the soil (and likely germination) by discouraging granivore attack. On the other hand, germination did not seem to have an important postdispersal impact on the persistence of P. flexuosa seeds in the soil. Both direct and indirect interactions between vertebrate herbivores and...
Constraints to wood-fired power plants larger than 50 MW stem from the inability to obtain sustainable forest by-products within a 100-km (60-mile) haul. Intensively managed biomass farms that produce 16 t ha−1 year−1 (7 dry tons acre−1 year−1) can support a 500-MW generating facility or a large petrochemical plant on a renewable basis with a biomass farm of 22-km (14-mile) radius. Selected strains of arid-adapted nitrogen-fixing trees of the genus Prosopis (mesquite) have achieved yields of 14·5 t ha−1 year−1; in Texas natural Prosopis stands occur on 22 million ha (55 million acres). Prosopis also occurs on semi-arid lands of Africa, South America, and the Far East. Managed biomass farms of Prosopis would be capable of supporting large petrochemical or electrical generating facilities with fuel costs less than either oil, gas, or coal in Texas. Wood-fired conversion facilities produce negligible SO2, little NOx, and no radioactive waste; the ash can be recycled on biomass farms, which should be less objectionable than strip mines.
The need for adequate supplies of correctly named, site-identified seed of trees grown for non-industrial purposes, e.g. fuelwood, fodder, shade, fences etc., in the dry zones of the tropics is now generally realised. This paper describes a programme at the Commonwealth Forestry Institute to collect the seed of non-industrial woody species native to Central America and neighbouring regions of South America. The seed of 25 species, of which 21 belong to the Leguminosae (some little-known botanically) has already been collected. The species include: Acacia deamii, A. farnesiana, A. pennatula, Albizia guachepele, Apoplanesia paniculata, Ateleia herbert-smithii, Caesalpinia coriaria, C. eriostachys, C. velutina, Enterolobium cyclocarpum, Gliricidia sepium, Haematoxylon brasiletto, Leucaena diversifolia, L. leucocephala, L. shannoni, Mimosa tenuiflora, Myrospermum frutescens, Parkinso- nia aculeata, Pithecellobium dulce, Prosopis juliflora, Senna atomaria, and (non-Leguminosae) Alvaradoa amorphoides, Crescentia alata, Guazuma ulmifolia, and Simarouba glauca. The characteristics, properties and distributions of the parent trees are described in detail for each of the above species. Methods of seed collection and extraction are discussed, together with problems of seed pre-treatment, weediness and genertic conservation.
Woody members of the Leguminosae are being introduced and planted as exotics on an unprecedented scale throughout the tropics. These multiple-use trees have an important role in social forestry, agroforestry and land reclamation schemes. They are especially suited to planting on harsh degraded sites, being fast growing, readily established and managed. In many cases they fix nitrogen and improve the soil. Such introductions have not always been beneficial in the past since they caused many severe weediness problems that necessitated expensive control programmes. Poor performance and low species adaptability must also be regarded as costs. The biological factors which constitute the adaptive weedy syndrome are discussed and it is shown that some woody legumes exhibit particularly aggressive combinations of frequent early flowering, successful seed dispersal and seed longevity. It is shown that although plant biology may determine weediness potential, the actual perception of a plant as a weed or as an asset is controlled by a combination of site and socio-economic factors and land management practices. A more rational approach to species introductions through logical consideration of plant biology, site factors and management is outlined and ideas for indices of weediness hazard and introduction potential are discussed. Lack of knowledge prior to introduction often presents an obstacle to implementing these ideas. The weediness tendencies of 146 species are listed.