Pedro Valverde - Academia.edu (original) (raw)

Papers by Pedro Valverde

Research paper thumbnail of Proteolysis with trypsin of mammalian tyrosinase isoforms from B16 mouse melanoma*1

Archives of Biochemistry and Biophysics, 1992

Research paper thumbnail of Population variation in the cost and benefit of tolerance and resistance against herbivory in Datura

Research paper thumbnail of EVOLUTION OF MIXED STRATEGIES OF PLANT DEFENSE ALLOCATION AGAINST NATURAL ENEMIES

Research paper thumbnail of The Evolution of Resistance and Tolerance to Herbivores

Annual Review of Ecology Evolution and Systematics, 2007

Research paper thumbnail of POPULATION VARIATION IN THE COST AND BENEFIT OF TOLERANCE AND RESISTANCE AGAINST HERBIVORY IN DATURA STRAMONIUM

Research paper thumbnail of Defensive role of leaf trichomes in resistance to herbivorous insects in Datura stramonium

Journal of Evolutionary Biology, 2001

Research paper thumbnail of Evolutionary ecology of Datura stramonium: equal plant fitness benefits of growth and resistance against herbivory

Journal of Evolutionary Biology, 2003

Research paper thumbnail of POPULATION VARIATION IN THE COST AND BENEFIT OF TOLERANCE AND RESISTANCE AGAINST HERBIVORY IN DATURA STRAMONIUM

Evolution, 2004

Abstract .–In this study we examine the hypothesis that divergent natural selection produces gene... more Abstract .–In this study we examine the hypothesis that divergent natural selection produces genetic differentiation among populations in plant defensive strategies (tolerance and resistance) generating adaptive variation in defensive traits against herbivory. Controlled genetic material (paternal half-sib families) from two populations of the annual Datura stramonium genetically differentiated in tolerance and resistance to herbivory were used. This set of paternal half-sib families was planted at both sites of origin and the pattern of genotypic selection acting on tolerance and resistance was determined, as well as the presence and variation in the magnitude of allocational costs of tolerance. Selection analyses support the adaptive differentiation hypothesis. Tolerance was favored at the site with higher average level of tolerance, and resistance was favored at the site with higher average level of resistance. The presence of significant environmentally dependent costs of tolerance was in agreement with site variation in the adaptive value of tolerance. Our results support the expectation that environmentally dependent costs of plant defensive strategies can generate differences among populations in the evolutionary trajectory of defensive traits and promote the existence of a selection mosaic. The pattern of contrasting selection on tolerance suggests that, in some populations of D. stramonium, tolerance may alter the strength of reciprocal coevolution between plant resistance and natural enemies.

Research paper thumbnail of Distribution of Peucetia viridans (Araneae: Oxyopidae) on Croton ciliatoglandulifer

Environmental Entomology, 2010

Research paper thumbnail of Habitat restriction in Mammillaria pectinifera, a threatened endemic Mexican cactus

Journal of Vegetation Science, 2003

Research paper thumbnail of Non weaving spiders on native woodlands and Eucalyptus plantations in Western Mexico: diversity and distribution patterns

Journal of Insect Conservation, 2010

Eucalyptus spp. are commonly planted, forming non-native plantations, including the tropics and t... more Eucalyptus spp. are commonly planted, forming non-native plantations, including the tropics and their wildlife conservation value is relatively unknown. Recent studies have concluded that secondary forests and tree plantations are less diverse than well-developed tropical rain forests. However, introduced Eucalyptus stands harbored similar species richness to surrounding native woodland in temperate woodlands in North America though the identity of the species present may differ. Species composition, as well as dominance curves and differences in community structure add additional insight to understanding faunistic responses to replacement of native woodland by Eucalyptus plantations. Here, we compared species richness, diversity patterns, and the distribution of non-weaving spiders between native woodlands and Eucalyptus plantations in a temperate region of Mexico. We found more Lycosidae species in all plantation stands. Other community attributes were not consistently different between plantations and native woodlands. This is explained by similarities between, and differences within, the understory of the two main vegetation types. Multivariate analyses identified three spider groups and five spider species could be identified as indicators of these groups. A comparison of the number of species of the wandering spiders between the two vegetation types suggests a compensation pattern that is reported here for the first time.

Research paper thumbnail of Assessing the ecological status of Mammillaria pectinifera Weber (Cactaceae), a rare and threatened species endemic of the Tehuacán-Cuicatlán Region in Central Mexico

Journal of Arid Environments, 2006

Research paper thumbnail of Habitat restriction in Mammillaria pectinifera , a threatened endemic Mexican cactus

Journal of Vegetation Science, 2003

Abstract. This study deals with the habitat restriction of Mammillaria pectinifera, a threatened ... more Abstract. This study deals with the habitat restriction of Mammillaria pectinifera, a threatened cactus species, confined to a few low density localities of the Tehuacán valley in tropical Mexico. We analysed the patterns of presence/absence of M. pectinifera in relation to the presence/absence of 48 other plant species, and the variation of environmental factors in 120 sampling plots. A Principal Components Analysis revealed a clear segregation between plots with and without individuals of M. pectinifera. A classification analysis resulted in four groups: two with low prevalence and two with high prevalence of M. pectinifera. Paired comparisons between plots with and without M. pectinifera allowed the characterization of its patterns of occurrence related to the variation of environmental factors. M. pectinifera was found on deep alkaline soils with relatively high surface stoniness and high water retention capacity, showing low species richness compared with plots where it was absent. The limited distribution of M. pectinifera in the Tehuacán Valley seems to be related to particular requirements of this species, being restricted to certain suitable habitat patches. Nevertheless, it is likely that other aspects, such as poor dispersal and establishment abilities, or biotic interactions could be associated with the observed patterns.

Research paper thumbnail of Stem tilting, pseudocephalium orientation, and stem allometry in Cephalocereus columna-trajani along a short latitudinal gradient

Plant Ecology, 2007

Cephalocereus columna-trajani is a giant columnar cactus endemic of the Tehuacán-Cuicatlán Valley... more Cephalocereus columna-trajani is a giant columnar cactus endemic of the Tehuacán-Cuicatlán Valley in Central Mexico. Stem tilting and northward pseudocephalium azimuth in C.␣columna-trajani have functional advantages in terms of interception of direct solar radiation at the northernmost portions of its range. Since the success of both characters strongly depends on the apparent position of the sun during the growing season, in this paper we test the hypothesis that the occurrence of such columnar morphology is restricted geographically and imposes mechanical restrictions that limit column height. Following a latitudinal gradient along the Tehuacán-Cuicatlán Valley, we selected five populations, recorded tilting angle and pseudocephalium azimuth, and carried out allometric and biomechanical analyses of height–diameter relationships. Northern populations showed higher tilting angles. Pseudocephalium azimuth significantly differed among populations, and pseudocephalium orientation was consistently North-Northwestern. Stem allometry showed that the stems of the southern populations increased in height at a far greater rate with respect to diameter than the northern populations. The southernmost population showed the lowest safety factor. These results support the hypothesis that stem tilting in C.␣columna-trajani is functionally advantageous in a restricted geographical range, and imposes mechanical restrictions to column height.

Research paper thumbnail of A natural hybrid population between Neobuxbaumia tetetzo and Cephalocereus columna-trajani (Cactaceae

Journal of Arid Environments, 1996

Research paper thumbnail of A morphometric analysis of a putative hybrid between Agave marmorata Roezl and Agave kerchovei Lem.: Agave peacockii Croucher

Botanical Journal of The Linnean Society, 1996

A supposed hybrid population (Agave peacockii) between Agave marmorata and Agave kerchovei in a s... more A supposed hybrid population (Agave peacockii) between Agave marmorata and Agave kerchovei in a semiarid ecosystem at Zapotitlán Salinas, in the Mexican State of Puebla, was investigated, and its hybrid status corroborated in morphometric terms. A Stepwise Discriminant Analysis of the ratios: Number of leaved Rosette diameter, Leaf width/Leaf length, Number of spines/Leaf length, Distance between the upper spine and the tip of the leaf/Leaf length, and Distance between the upper spine and the tip of the leaf/Number of spines, supported our hypothesis of the existence of these naturally occurring hybrids, which are intermediate and distinct from the parental species. A null model was constructed to contrast the real case with a possible artifact, and the results also supported our hypothesis. The possible meaning of this kind of hybridization is discussed.

Research paper thumbnail of Influence of leaf-cutting ants ( Atta mexicana) on performance and dispersion patterns of perennial desert shrubs in an inter-tropical region of Central Mexico

Journal of Arid Environments, 2000

The influence of defoliation by leaf-cutting ants (Atta mexicana) on the dispersion patterns of x... more The influence of defoliation by leaf-cutting ants (Atta mexicana) on the dispersion patterns of xerophytic shrubs in the semi-arid valley of Zapotitlán, Mexico was analysed. All shrubs and ant nest entrances were mapped in a 65×50 m stand, and the vigour of each individual shrub was estimated. A regression analysis between the distance to the nearest nest and the vigour of plants showed a significant relationship for Acacia constricta, Castela tortuosa,Echinopteryx eglandulosa and Mimosa luisana, revealing higher vigour as distance to the nest entrances increases. A point pattern analysis showed a clear clumped pattern for the latter three species, plus Prosopis laevigata; whereasAcacia constricta and Cercidium praecox, as well as the ant nest entrances, did not show any pattern significantly different from chance. A bivariate point pattern analysis did not show the expected repulsion pattern among shrubs and nest entrances. According to an auto-correlation analysis, individuals of Mimosa luisana forming dense clusters away from the ant nests entrances showed higher vigour values than those plants with higher inter-individual distances closer to the nests entrances. Although the unveiling of the ecological implications of ant–shrub and shrub–shrub interactions demands a detailed experimental approach, our results reveal the importance of herbivory in the structuring of natural communities.

Research paper thumbnail of A morphometric analysis of a putative hybrid between Agave marmorata Roezl and Agave kerchovei Lem.: Agave peacockii Croucher

Botanical Journal of The Linnean Society, 1996

Research paper thumbnail of Proteolysis with trypsin of mammalian tyrosinase isoforms from B16 mouse melanoma*1

Archives of Biochemistry and Biophysics, 1992

Research paper thumbnail of Population variation in the cost and benefit of tolerance and resistance against herbivory in Datura

Research paper thumbnail of EVOLUTION OF MIXED STRATEGIES OF PLANT DEFENSE ALLOCATION AGAINST NATURAL ENEMIES

Research paper thumbnail of The Evolution of Resistance and Tolerance to Herbivores

Annual Review of Ecology Evolution and Systematics, 2007

Research paper thumbnail of POPULATION VARIATION IN THE COST AND BENEFIT OF TOLERANCE AND RESISTANCE AGAINST HERBIVORY IN DATURA STRAMONIUM

Research paper thumbnail of Defensive role of leaf trichomes in resistance to herbivorous insects in Datura stramonium

Journal of Evolutionary Biology, 2001

Research paper thumbnail of Evolutionary ecology of Datura stramonium: equal plant fitness benefits of growth and resistance against herbivory

Journal of Evolutionary Biology, 2003

Research paper thumbnail of POPULATION VARIATION IN THE COST AND BENEFIT OF TOLERANCE AND RESISTANCE AGAINST HERBIVORY IN DATURA STRAMONIUM

Evolution, 2004

Abstract .–In this study we examine the hypothesis that divergent natural selection produces gene... more Abstract .–In this study we examine the hypothesis that divergent natural selection produces genetic differentiation among populations in plant defensive strategies (tolerance and resistance) generating adaptive variation in defensive traits against herbivory. Controlled genetic material (paternal half-sib families) from two populations of the annual Datura stramonium genetically differentiated in tolerance and resistance to herbivory were used. This set of paternal half-sib families was planted at both sites of origin and the pattern of genotypic selection acting on tolerance and resistance was determined, as well as the presence and variation in the magnitude of allocational costs of tolerance. Selection analyses support the adaptive differentiation hypothesis. Tolerance was favored at the site with higher average level of tolerance, and resistance was favored at the site with higher average level of resistance. The presence of significant environmentally dependent costs of tolerance was in agreement with site variation in the adaptive value of tolerance. Our results support the expectation that environmentally dependent costs of plant defensive strategies can generate differences among populations in the evolutionary trajectory of defensive traits and promote the existence of a selection mosaic. The pattern of contrasting selection on tolerance suggests that, in some populations of D. stramonium, tolerance may alter the strength of reciprocal coevolution between plant resistance and natural enemies.

Research paper thumbnail of Distribution of Peucetia viridans (Araneae: Oxyopidae) on Croton ciliatoglandulifer

Environmental Entomology, 2010

Research paper thumbnail of Habitat restriction in Mammillaria pectinifera, a threatened endemic Mexican cactus

Journal of Vegetation Science, 2003

Research paper thumbnail of Non weaving spiders on native woodlands and Eucalyptus plantations in Western Mexico: diversity and distribution patterns

Journal of Insect Conservation, 2010

Eucalyptus spp. are commonly planted, forming non-native plantations, including the tropics and t... more Eucalyptus spp. are commonly planted, forming non-native plantations, including the tropics and their wildlife conservation value is relatively unknown. Recent studies have concluded that secondary forests and tree plantations are less diverse than well-developed tropical rain forests. However, introduced Eucalyptus stands harbored similar species richness to surrounding native woodland in temperate woodlands in North America though the identity of the species present may differ. Species composition, as well as dominance curves and differences in community structure add additional insight to understanding faunistic responses to replacement of native woodland by Eucalyptus plantations. Here, we compared species richness, diversity patterns, and the distribution of non-weaving spiders between native woodlands and Eucalyptus plantations in a temperate region of Mexico. We found more Lycosidae species in all plantation stands. Other community attributes were not consistently different between plantations and native woodlands. This is explained by similarities between, and differences within, the understory of the two main vegetation types. Multivariate analyses identified three spider groups and five spider species could be identified as indicators of these groups. A comparison of the number of species of the wandering spiders between the two vegetation types suggests a compensation pattern that is reported here for the first time.

Research paper thumbnail of Assessing the ecological status of Mammillaria pectinifera Weber (Cactaceae), a rare and threatened species endemic of the Tehuacán-Cuicatlán Region in Central Mexico

Journal of Arid Environments, 2006

Research paper thumbnail of Habitat restriction in Mammillaria pectinifera , a threatened endemic Mexican cactus

Journal of Vegetation Science, 2003

Abstract. This study deals with the habitat restriction of Mammillaria pectinifera, a threatened ... more Abstract. This study deals with the habitat restriction of Mammillaria pectinifera, a threatened cactus species, confined to a few low density localities of the Tehuacán valley in tropical Mexico. We analysed the patterns of presence/absence of M. pectinifera in relation to the presence/absence of 48 other plant species, and the variation of environmental factors in 120 sampling plots. A Principal Components Analysis revealed a clear segregation between plots with and without individuals of M. pectinifera. A classification analysis resulted in four groups: two with low prevalence and two with high prevalence of M. pectinifera. Paired comparisons between plots with and without M. pectinifera allowed the characterization of its patterns of occurrence related to the variation of environmental factors. M. pectinifera was found on deep alkaline soils with relatively high surface stoniness and high water retention capacity, showing low species richness compared with plots where it was absent. The limited distribution of M. pectinifera in the Tehuacán Valley seems to be related to particular requirements of this species, being restricted to certain suitable habitat patches. Nevertheless, it is likely that other aspects, such as poor dispersal and establishment abilities, or biotic interactions could be associated with the observed patterns.

Research paper thumbnail of Stem tilting, pseudocephalium orientation, and stem allometry in Cephalocereus columna-trajani along a short latitudinal gradient

Plant Ecology, 2007

Cephalocereus columna-trajani is a giant columnar cactus endemic of the Tehuacán-Cuicatlán Valley... more Cephalocereus columna-trajani is a giant columnar cactus endemic of the Tehuacán-Cuicatlán Valley in Central Mexico. Stem tilting and northward pseudocephalium azimuth in C.␣columna-trajani have functional advantages in terms of interception of direct solar radiation at the northernmost portions of its range. Since the success of both characters strongly depends on the apparent position of the sun during the growing season, in this paper we test the hypothesis that the occurrence of such columnar morphology is restricted geographically and imposes mechanical restrictions that limit column height. Following a latitudinal gradient along the Tehuacán-Cuicatlán Valley, we selected five populations, recorded tilting angle and pseudocephalium azimuth, and carried out allometric and biomechanical analyses of height–diameter relationships. Northern populations showed higher tilting angles. Pseudocephalium azimuth significantly differed among populations, and pseudocephalium orientation was consistently North-Northwestern. Stem allometry showed that the stems of the southern populations increased in height at a far greater rate with respect to diameter than the northern populations. The southernmost population showed the lowest safety factor. These results support the hypothesis that stem tilting in C.␣columna-trajani is functionally advantageous in a restricted geographical range, and imposes mechanical restrictions to column height.

Research paper thumbnail of A natural hybrid population between Neobuxbaumia tetetzo and Cephalocereus columna-trajani (Cactaceae

Journal of Arid Environments, 1996

Research paper thumbnail of A morphometric analysis of a putative hybrid between Agave marmorata Roezl and Agave kerchovei Lem.: Agave peacockii Croucher

Botanical Journal of The Linnean Society, 1996

A supposed hybrid population (Agave peacockii) between Agave marmorata and Agave kerchovei in a s... more A supposed hybrid population (Agave peacockii) between Agave marmorata and Agave kerchovei in a semiarid ecosystem at Zapotitlán Salinas, in the Mexican State of Puebla, was investigated, and its hybrid status corroborated in morphometric terms. A Stepwise Discriminant Analysis of the ratios: Number of leaved Rosette diameter, Leaf width/Leaf length, Number of spines/Leaf length, Distance between the upper spine and the tip of the leaf/Leaf length, and Distance between the upper spine and the tip of the leaf/Number of spines, supported our hypothesis of the existence of these naturally occurring hybrids, which are intermediate and distinct from the parental species. A null model was constructed to contrast the real case with a possible artifact, and the results also supported our hypothesis. The possible meaning of this kind of hybridization is discussed.

Research paper thumbnail of Influence of leaf-cutting ants ( Atta mexicana) on performance and dispersion patterns of perennial desert shrubs in an inter-tropical region of Central Mexico

Journal of Arid Environments, 2000

The influence of defoliation by leaf-cutting ants (Atta mexicana) on the dispersion patterns of x... more The influence of defoliation by leaf-cutting ants (Atta mexicana) on the dispersion patterns of xerophytic shrubs in the semi-arid valley of Zapotitlán, Mexico was analysed. All shrubs and ant nest entrances were mapped in a 65×50 m stand, and the vigour of each individual shrub was estimated. A regression analysis between the distance to the nearest nest and the vigour of plants showed a significant relationship for Acacia constricta, Castela tortuosa,Echinopteryx eglandulosa and Mimosa luisana, revealing higher vigour as distance to the nest entrances increases. A point pattern analysis showed a clear clumped pattern for the latter three species, plus Prosopis laevigata; whereasAcacia constricta and Cercidium praecox, as well as the ant nest entrances, did not show any pattern significantly different from chance. A bivariate point pattern analysis did not show the expected repulsion pattern among shrubs and nest entrances. According to an auto-correlation analysis, individuals of Mimosa luisana forming dense clusters away from the ant nests entrances showed higher vigour values than those plants with higher inter-individual distances closer to the nests entrances. Although the unveiling of the ecological implications of ant–shrub and shrub–shrub interactions demands a detailed experimental approach, our results reveal the importance of herbivory in the structuring of natural communities.

Research paper thumbnail of A morphometric analysis of a putative hybrid between Agave marmorata Roezl and Agave kerchovei Lem.: Agave peacockii Croucher

Botanical Journal of The Linnean Society, 1996