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1 Gaps in the forest canopy allow establishment of many understorey species. As gaps close, their demographic behaviour is affected by changing environmental conditions. A demographic analysis of Primula vulgaris populations in forest... more
1 Gaps in the forest canopy allow establishment of many understorey species. As gaps close, their demographic behaviour is affected by changing environmental conditions. A demographic analysis of Primula vulgaris populations in forest patches with varying canopy openness was carried out to investigate the effect of forest canopy dynamics on the demography of this forest understorey herb. 2 Eight P. vulgaris populations across a range of light conditions were studied in three deciduous temperate forests in Britain. Demographic data were collected in each population during summer 1992, 1993 and 1994, and stage‐based population projection matrices were built to describe their demography for two growth periods (1992–93 and 1993–94). 3 Population growth rate (λ) varied from 0.97 to 1.98 in 1992–93, and from 0.88 to 1.23 in 1993–94. There was a significant positive correlation between λ and diffuse light for the two periods studied: generally, population growth rate was lower in darker patches, implying that populations decline as the canopy closes. Lower λ‐values in 1993–94 were the result of increased mortality and decreased fecundity compared to 1992–93. In most cases the observed population structures were significantly different from the calculated stable‐stage distributions. 4 Sensitivity analysis showed that λ was most sensitive to changes in matrix transitions that corresponded to growth from small to adult stages, especially those that implied fast growth. Elasticity analysis revealed that the contribution of fecundity elements to λ was small, but populations in brighter patches showed comparatively higher fecundity elasticities than populations under the closed canopy. High elasticities corresponded to the entries that implied growth (especially in brighter patches) or persistence in adult categories (predominantly in darker patches). 5 The observed variation in the demography of P. vulgaris in different patches along the forest regeneration cycle stresses the importance of studying the variation in plant population dynamics across the range of habitat patches in which the plant naturally occurs.
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... The effect these changes have on the demogra-phy of herb populations is unknown, in particular, the way in which different phases of their life cycle are affected as canopy ... Four replicates of 25 seeds per population were set in... more
... The effect these changes have on the demogra-phy of herb populations is unknown, in particular, the way in which different phases of their life cycle are affected as canopy ... Four replicates of 25 seeds per population were set in Petri dishes with wet filter paper in a green-house ...
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Research Interests: Geography, Forest Ecology And Management, IT Management, Forest Ecology, Biological Sciences, and 12 moreTropical trees, Environmental Sciences, Tropics, Tropical forest, Tropical Dry Forest, Adaptive Management, Forest Products, Population dynamic, Dry Tropical Forest, Matrix Model, Population Growth Rate, and Burseraceae
Eradication of herbivores, due to human disturbances, produces a demographic outburst of highly competitive prey species, which in turn reduces plant species diversity. This happens at Los Tuxtlas tropical rainforest, Mexico, where a... more
Eradication of herbivores, due to human disturbances, produces a demographic outburst of highly competitive prey species, which in turn reduces plant species diversity. This happens at Los Tuxtlas tropical rainforest, Mexico, where a population outburst of the understory palm Astrocaryum mexicanum is ostensibly excluding tree species, but how this is occurring is still unknown. We used a neighborhood approach to explore the effects of palm shading and palm crowding on the survival and growth (RGR) of saplings of six common tree species. Sixteen to 32 saplings (1.5–2.5 m height) per species were used as focal individuals of circular neighborhoods (4 m radius), which included palms ≥ 1cm stem length potentially competing for light or soil resources. Shading was estimated using hemispherical photographs. Overall, survivorship was high combining all species (93.8%/yr). In most species, shading produced a displacement of the crown, which increased with specific leaf area of species. In three species, shading had a negative effect on RGR without any effect of crowding, the contrary occurred in two species, and in one species no effects were found. No effects due to trees (DBH ≥1cm) crowding were detected. The shading effect increased with species leaf dry matter content (LDMC), while the effect of crowding declined with LDMC and increased with sapling total leaf area. We argue that the species‐dependent palm shading/crowding effects were related to the shade tolerance of sapling species. In the long‐term, such species‐specific responses could have consequences for forest structure and composition, as saplings develop to mature stages.
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BLDSC reference no.: DX188611. Thesis (doctoral)--Open University, 1995.
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:Knowledge of the population dynamics of tropical trees has expanded considerably in the past 20 years. An important observation deriving from these investigations is the confirmation that population behaviour varies both in time and... more
:Knowledge of the population dynamics of tropical trees has expanded considerably in the past 20 years. An important observation deriving from these investigations is the confirmation that population behaviour varies both in time and space. A tool recently developed to evaluate the potential for variation in vital rates, and therefore in population growth rate, is variance-standardized perturbation analysis (VSPA). In this paper we report the results of a 2-y demographic analysis of a population of the tropical treeManilkara zapotain a subtropical rain forest in the Mexican state of Veracruz, in which variance-standardized perturbation analysis was applied and compared with the results of the traditional elasticity analyses. To build population projection matrices, we tagged and followed a sample of 91 juvenile and adult individuals, and 635 seedlings. We subdivided the sample in nine size classes (defined by tree height and dbh; as well as leaf size, in the case of seedlings) and estimated transition probabilities and fecundity for each class. The demography ofM. zapotavaried greatly from the first to the second year of study (in 1998–1999, λ = 0.987, while in 1999–2000, λ = 1.038) due to negligible seed production during the first year and a massive reproductive event during the second. The largest elasticity values for both years corresponded to persistence of large juveniles and adults. Although the fecundity entries showed very low elasticity values, the variance-standardized perturbation analysis revealed the importance of these matrix entries; transition to larger categories and retrogression to smaller ones of saplings and juveniles were also important demographic processes contributing to variation in λ according to the VSPA. Thus, although the results of elasticity analysis and VSPA were similar for the 1998–1999 matrix, they differed substantially for the 1999–2000 matrix. In the latter, the VSPA enhanced the importance of demographic processes that are intuitively relevant for the population studied. This points toward the necessity of further exploring the use of VSPA, since it offers several advantages over the traditional elasticity analysis: it concentrates on the impact on λ of vital rates that actually vary, and the interpretation of the results is more realistic and straightforward.
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Epiphytic angiosperms represent ca. 10 % of the world's flowering plants and are key elements in tropical forests. Here we synthesize the available literature on their population ecology in an attempt to find patterns that may... more
Epiphytic angiosperms represent ca. 10 % of the world's flowering plants and are key elements in tropical forests. Here we synthesize the available literature on their population ecology in an attempt to find patterns that may characterize them. Epiphytes tend to have specialized pollination systems frequently involving animal vectors, resulting in a mixture of selfing and outcrossing that ensures abundant seed production. Seed dispersal is anemochorous in 84 % of the species and is pivotal for the establishment of new local populations within metapopulation. Seed germination is highly dependent on specific environmental conditions, resulting in seedling establishment in particular microhabitats on phorophytes. Individual growth rates are slow and limited by the low water and nutrient availability characteristic of the epiphytic habitat. Population growth rates (λ) are close to unity and depend mostly on the survival of adults. This plant group is highly vulnerable to habitat lo...
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Background: Reproductive traits are features of a species’ biology that may determine its rarity, as they affect its genetic diversity and structure, as well as its population dynamics.Study species: The rare and threatened species... more
Background: Reproductive traits are features of a species’ biology that may determine its rarity, as they affect its genetic diversity and structure, as well as its population dynamics.Study species: The rare and threatened species Furcraea parmentieri, whose distribution is limited to the Trans-Mexican volcanic belt. Questions: How is the reproductive phenology of F. parmentieri? Does flower morphology vary between individuals? Does it produce nectar? Which animals visit its flowers? Is it self-compatible? Do the seeds originated via different pollination treatments show differences in their germinability?Study sites and dates: We studied the F. parmentieri from 2007 to 2008, at El Xitle volcano (altitude: 2800 – 3100 m; pine-oak forest), in the south of Mexico City.Methods: Reproductive phenology was recorded through fortnightly visits to the study site. Flowers were collected, flower visitors were recorded and nectar production was measured. An experiment was done which included ...
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Many epiphytic orchids are harvested in Mexico for different purposes. Laelia fur-furacea is one of the most intensively traded species. Its inflorescences are used as ornaments during the December festivities. We investigated the effect... more
Many epiphytic orchids are harvested in Mexico for different purposes. Laelia fur-furacea is one of the most intensively traded species. Its inflorescences are used as ornaments during the December festivities. We investigated the effect of severing the flowering pseudobulb. This is the traditional technique frequently used by collectors at the study area. We wished to investigate its effects on the production of new pseudobulbs, as well as on their size and flowering probability. Also, we examined the survival probability and growth of individuals that had fallen on the ground to evaluate their potential as trading resources. Inflorescence collection did not affect the production of new pseudobulbs the following season. However, it affected the size of these pseudobulbs, as well as their flowering probability. Yet, the direction of this effect was not consistent between years. Nearly six percent of all L. furfuracea plants at the study site were found on the ground. Over 80 percent of them survived for at least two years, although most of them showed pseudobulb loss over that period of time. We conclude that harvesting of flowering pseudobulbs may be sustainable in terms of its effects on plant performance, at least in the short term. The active management of plants that have fallen on the ground may reduce the harvesting pressure on natural populations. Harvesting of flowering pseudobulbs may diminish some aspects of plant performance, but its effects need to be evaluated with complete life cycle data and take into account interannual variation in vital rates. Abstract in Spanish is available with online material K E Y W O R D S
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Although most vascular epiphytes are generalist, some exhibit host preferences. The latter may vary spatio-temporally driven by variation in environmental conditions. However, to our knowledge no previous studies have evaluated this... more
Although most vascular epiphytes are generalist, some exhibit host preferences. The latter may vary spatio-temporally driven by variation in environmental conditions. However, to our knowledge no previous studies have evaluated this variation. The aim of this study was to analyze variation in host preferences and population structures in the endangered bromeliad Tillandsia carlos-hankii in two pine-oak forests which differ in environmental conditions, tree composition and community structure. Our questions were: i) does Tillandsia carlos-hankii prefer certain host species over others?; ii) does this preference vary between sites?; iii) how does population structure vary between hosts species and sites? The two sites chosen were an east-facing (I NE) and a west-facing slope (C NW). The tree community was sampled within an area of 0.1 ha at each site. Preferred host species were identified using two criteria: a) the degree of colonization; and b) the probability of colonization. In addition, population size-structure on each colonized tree was evaluated to compare between sites and host species. The results showed that almost every tree in the community was colonized by this bromeliad. At both sites Quercus rugosa was a preferred host species, while Q. laurina and Mirsyne juergensenii were preferred at I NE but limiting at C NW. In turn, Pinus teocote was limiting at both sites. The percentage of small trees that were colonized depended on species identity. Population structures differed between sites and host species. Thus, both host preferences and local population behavior vary spatially given the differential conditions associated with the two sites.
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Although most vascular epiphytes are generalist, some exhibit host preferences. The latter may vary spatio-temporally driven by variation in environmental conditions. However, to our knowledge no previous studies have evaluated this... more
Although most vascular epiphytes are generalist, some exhibit host preferences. The latter may vary spatio-temporally driven by variation in environmental conditions. However, to our knowledge no previous studies have evaluated this variation. The aim of this study was to analyze variation in host preferences and population structures in the endangered bromeliad Tillandsia carlos-hankii in two pine-oak forests which differ in environmental conditions, tree composition and community structure. Our questions were: i) does Tillandsia carlos-hankii prefer certain host species over others?; ii) does this preference vary between sites?; iii) how does population structure vary between hosts species and sites? The two sites chosen were an east-facing (I NE) and a west-facing slope (C NW). The tree community was sampled within an area of 0.1 ha at each site. Preferred host species were identified using two criteria: a) the degree of colonization; and b) the probability of colonization. In ad...
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... Teresa Valverdet, Irene Pisantyt and Emmanuel Rinc6nt ... Three species are characteristic of beach areas of central Gulf of Mexico (Ipomoea pes-caprae, Canavalia rosea and Palafoxia lindenii) while the other three occupy mobile and... more
... Teresa Valverdet, Irene Pisantyt and Emmanuel Rinc6nt ... Three species are characteristic of beach areas of central Gulf of Mexico (Ipomoea pes-caprae, Canavalia rosea and Palafoxia lindenii) while the other three occupy mobile and semi-mobile inner dunes (Chamaecrista ...
Research Interests: Plasticity and Coastal
Research Interests: Earth Sciences, Biomass, Arid environments, Phenotypic Plasticity, Biological Sciences, and 14 moreRelative Growth Rate, Growth, Environmental Sciences, Soil moisture, Rare species, Factorial Design, Growth Analysis, Biomass Allocation, Solar radiation, Environmental Conditions, Seedling Establishment, Experimental Tests, Seedling Growth, and Nurse plant
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ABSTRACT
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... The effect these changes have on the demogra-phy of herb populations is unknown, in particular, the way in which different phases of their life cycle are affected as canopy ... Four replicates of 25 seeds per population were set in... more
... The effect these changes have on the demogra-phy of herb populations is unknown, in particular, the way in which different phases of their life cycle are affected as canopy ... Four replicates of 25 seeds per population were set in Petri dishes with wet filter paper in a green-house ...