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Reproductive Size (reproductive + size)

Distribution by Scientific Domains

Life Sciences	100%

Selected Abstracts

Comparative fire ecology of tropical savanna and forest trees

FUNCTIONAL ECOLOGY, Issue 6 2003
William A. Hoffmann
Summary 1Fire is important in the dynamics of savanna,forest boundaries, often maintaining a balance between forest advance and retreat. 2We performed a comparative ecological study to understand how savanna and forest species differ in traits related to fire tolerance. We compared bark thickness, root and stem carbohydrates, and height of reproductive individuals within 10 congeneric pairs, each containing one savanna and one forest species. 3Bark thickness of savanna species averaged nearly three times that of forest species, thereby reducing the risk of stem death during fire. The allometric relationship between bark thickness and stem diameter differed between these two tree types, with forest species tending to have a larger allometric coefficient. 4The height of reproductive individuals of forest species averaged twice that of congeneric savanna species. This should increase the time necessary for forest species to reach reproductive size, thereby reducing their capacity to reach maturity in the time between consecutive fires. 5There was no difference in total non-structural carbohydrate content of stems or roots between savanna and forest species, though greater allocation to total root biomass by savanna species probably confers greater capacity to resprout following fire. 6These differences in fire-related traits may largely explain the greater capacity of savanna species to persist in the savanna environment. [source]

Mutualism, hybrid inviability and speciation in a tropical ant,plant

JOURNAL OF EVOLUTIONARY BIOLOGY, Issue 4 2008
G. LÉOTARD
Abstract Although biotic interactions are particularly intricate in the tropics, few studies have examined whether divergent adaptations to biotic interactions lead to speciation in tropical organisms. Ant,plant mutualisms are widespread in the tropics. Within Leonardoxa africana, two subspecies present contrasting defences against herbivores. Young leaves of subsp. africana are defended by mutualistic ants, whereas subsp. gracilicaulis satiates herbivores by synchronized leaf production. Subsp. africana possesses hollow internodes and many large foliar nectaries, housing and feeding ants. We detected no genetic introgression between the two subspecies in the contact zone between them. F1 hybrids were present. They were intermediate in phenotype, expressing reduced, nonfunctional but costly myrmecophilic traits. However, they suffered more herbivory than their parents. Hybrids remained small, failing to reach reproductive size, probably due to their maladapted defence phenotype. Hence, there could be a direct link between adaptation to mutualism and reproductive isolation: biotic interactions could be a driver of tropical diversity. [source]

Increased early growth rates decrease longevities of conifers in subalpine forests

OIKOS, Issue 8 2009
Christof Bigler
For trees, fast growth rates and large size seem to be a fitness benefit because of increased competitiveness, attainment of reproductive size earlier, reduction of generation times, and increased short-term survival chances. However, fast growth rates and large size entail reduced investment in defenses, lower wood density and mechanical strength, increased hydraulic resistance as well as problems with down-regulation of growth during periods of stress, all of which may decrease tree longevity. In this study, we investigated the relationship between longevity and growth rates of trees and quantified effects of spatial environmental variation (elevation, slope steepness, aspect, soil depth) on tree longevity. Radial growth rates and longevities were determined from tree-ring samples of 161 dead trees from three conifer species in subalpine forests of the Colorado Rocky Mountains (Abies lasiocarpa, Picea engelmannii) and the Swiss Alps (Picea abies). For all three species, we found an apparent tradeoff between growth rate to the age of 50 years and longevity (i.e. fast early growth is associated with decreased longevity). This association was particularly pronounced for larger P. engelmannii and P. abies, which attained canopy size, however, there were also significant effects for smaller P. engelmannii and P. abies. For the more shade-tolerant A. lasiocarpa, tree size did not have any effect. Among the abiotic variables tested only northerly aspect significantly favored longevity of A. lasiocarpa and P. engelmannii. Trees growing on south-facing aspects probably experience greater water deficits leading to premature tree death, and/or shorter life spans may reflect shorter fire intervals on these more xeric aspects. Empirical evidence from other studies has shown that global warming affects growth rates of trees over large spatial and temporal scales. For moist-cool subalpine forests, we hypothesize that the higher growth rates associated with global warming may in turn result in reduced tree longevity and more rapid turnover rates. [source]

Spatial and temporal variation in the fruiting phenology of palms in isolated stands

PLANT SPECIES BIOLOGY, Issue 1 2008
GREGORY H. ADLER
Abstract Fruiting phenologies of two species of palms, Astrocaryum standleyanum L. H. Bailey and Attalea butyracea (Mutis ex L. f) Wess. Boer, isolated on eight small (1.7,3.7 ha) forested islands in the Panama Canal were studied over a 33-month period. Individual palms were permanently marked with numbered aluminum tags and censused each month for the presence of ripe fruits. The dataset consisted of 1106 monthly observations of palms with ripe fruits among the 634 marked individuals. Mean densities of palms of reproductive size varied widely among islands, ranging from a low of 0.3 ha,1 for A. standleyanum and 3.5 ha,1 for A. butyracea to a high of 44.9 ha,1 for A. standleyanum and 33.7 ha,1 for A. butyracea. Both species showed distinctly seasonal periods of fruiting activity that varied in duration between the two species and among years. The timing of fruiting by A. standleyanum was highly synchronous among islands, whereas inter-island synchrony in A. butyracea was less pronounced. The percentages of marked individuals that fruited varied widely among islands and years. Results indicated that these palms responded to both spatially and temporally variable conditions that promoted fruit production. We suggest that pollinator abundances are a crucial factor affecting reproductive output. Conditions that favor successful reproduction and seed dispersal, such as pollinator activity and the attraction of dispersal agents, may be the ultimate factors that have influenced the reproductive phenologies of these two species of palms. [source]

Succession and Micro-elevation Effects on Seedling Establishment of Calophyllum brasiliense Camb. (Clusiaceae) in an Amazonian River Meander Forest1

BIOTROPICA, Issue 4 2003
Rachel T. King
ABSTRACT I investigated the effects of successional stage and micro-elevation on seedling establishment of Calophyllum brasiliense (Clusiaceae), a common canopy tree of seasonally flooded lowland forest along the Manú River meander zone in southeastern Peru. To compare seedling establishment between microhabitat types, I planted C. brasiliense seeds in a fully crossed experimental design of three successional stages (early, mid, and mature) and two micro-elevations (levees and backwaters). Seedling establishment success in this study was affected by both successional stage and micro-elevation, but micro-elevation was most important in mid-successional habitats. In general, seedlings in early succession experienced better conditions than in mature forest; light levels were higher, herbivory lower, and seedling growth higher. In mid-successional forest, micro-elevation determined habitat quality; backwaters had higher light levels, lower herbivory, and higher seedling growth and survival than levees. Mid-successional backwaters were similar in quality to early successional forest for seedling establishment, while levees in that same successional stage were the poorest microhabitats for establishment. Although mid-successional backwaters are similar to early succession for seedling establishment, in the long run, seedlings that establish in mid-succession have a lower chance of reaching reproductive size before their habitat ages to mature forest than members of their cohort that established in early succession. I hypothesize that successful recruitment for C. brasiliense in the Manú River meander system requires dispersal to early successional habitat. RESUMEN Yo investingé el efecto de microhábitats del sistema serpentine ribereño, los cuales se diferencian en estado sucesional y en microelevación, en el establecimiento de plántulas de Calophyllum brasiliense (Clusiaceae), un árbol común en bosques estacionalmente inundados alrededor de los meandros del Río Manú en Perú. Para comparar establecimiento de plántulas entre los microhábitats, sembré semillas de C. brasiliense en seis condiciones de microhábitat, combinando los efectos de tres estados sucesionales (bosque temprano, mediano, y maduro) y dos microelevaciones (lomos y depresiones). El establecimiento de plántulas en este estudio fue afectado por estado sucesional y por microelevación, pero microelevación fue más importante en sucesión mediana. En general, plántulas en sucesión temprana tenían mejores condiciones que plántulas de bosque maduro; niveles de luz más altos, menor herbivoría, y una mayor tasa de crecimiento. En sucesión mediana, microelevacion determinó calidad de hábitat; depresiones presentaron más luz, menos herbivoria, y mayor crecimiento y sobreviviencia de plántulas que los lomos. Depresiones en sucesión mediano fueran similares en calidad a sucesión temprano en cuanto al establecimiento de plántulas, mientras que lomos en este mismo estado sucesional fueron los peores microhábitats para establecimiento. A largo plazo, las plántulas establecidas en sucesión mediano tienen menos probabilidad de alcanzar el tamaño reproductive (antes de que el hábitat llega a ser bosque maduro) que las plántulas de la misma edad, establecidas en sucesión temprana. El reclutamiento efectivo de C. brasiliense en el sistema serpentino del Río Manú probablemente requiere la dispersión al hábitat de sucesión temprana. [source]