RESUMO
Cities are home to several species of pollinators that play an important role in the reproductive success of wild and cultivated plants that grow in these ecosystems and their surroundings. Pollution is a main driver of pollinator decline. Light and noise pollution are more intense in cities than in any other ecosystem. Although nocturnal pollinators are heavily exposed to these pollutants, their effect on bat pollination is still unknown. Our goal was to assess the effect of light and noise pollution on the main pollination components (pollinator visits, pollen transfer, pollen germination, fruit, and seed set) of the tropical tree, Ceiba pentandra, in a heavily urbanized ecosystem. We measured these components in sites with contrasting intensities of artificial light and anthropogenic noise and statistically assessed the direct and indirect effect of pollutants on pollination components using structural equation modeling. We found that noise and light pollution negatively affected the visits by the bats that pollinate C. pentandra. However, these negative effects did not affect posterior pollination components. In fact, the direct effect of light pollution on reproductive success was positive and greater than the indirect effects via pollinator visits. We suggest that illuminated trees may be able to sustain a large quantity of fruits and seeds because they produce more photosynthates due to greater light radiation and delayed leaf abscission. We conclude that, despite the negative effect of light and noise on pollinator visits, these pollutants did not significantly impact the reproductive success of C. pentandra.
Assuntos
Quirópteros , Árvores , Animais , Ecossistema , Flores , Poluição Luminosa , Polinização , ReproduçãoRESUMO
Plant diversity can influence predators and omnivores and such effects may in turn influence herbivores and plants. However, evidence for these ecological feedbacks is rare. We evaluated if the effects of tree species (SD) and genotypic diversity (GD) on the abundance of different guilds of insect herbivores associated with big-leaf mahogany (Swietenia macrophylla) were contingent upon the protective effects of ants tending extra-floral nectaries of this species. This study was conducted within a larger experiment consisting of mahogany monocultures and species polycultures of four species and -within each of these two plot types- mahogany was represented by either one or four maternal families. We selected 24 plots spanning these treatment combinations, 10 mahogany plants/plot, and within each plot experimentally reduced ant abundance on half of the selected plants, and surveyed ant and herbivore abundance. There were positive effects of SD on generalist leaf-chewers and sap-feeders, but for the latter group this effect depended on the ant reduction treatment: SD positively influenced sap-feeders under ambient ant abundance but had no effect when ant abundance was reduced; at the same time, ants had negative effects on sap feeders in monoculture but no effect in polyculture. In contrast, SD did not influence specialist stem-borers or leaf-miners and this effect was not contingent upon ant reduction. Finally, GD did not influence any of the herbivore guilds studied, and such effects did not depend on the ant treatment. Overall, we show that tree species diversity influenced interactions between a focal plant species (mahogany) and ants, and that such effects in turn mediated plant diversity effects on some (sap-feeders) but not all the herbivores guilds studied. Our results suggest that the observed patterns are dependent on the combined effects of herbivore identity, diet breadth, and the source of plant diversity.
Assuntos
Formigas/fisiologia , Comportamento Animal , Ecossistema , Herbivoria/fisiologia , Insetos/fisiologia , Árvores , Animais , Biota , Florestas , Variação Genética , Genótipo , Controle de Insetos , Insetos/classificação , Meliaceae/genética , México , Dispersão Vegetal , Folhas de Planta , Especificidade da Espécie , Árvores/classificação , Árvores/genéticaRESUMO
Dimorphic cleistogamy is a specialized form of mixed mating system where a single plant produces both open, potentially outcrossed chasmogamous (CH) and closed, obligately self-pollinated cleistogamous (CL) flowers. Typically, CH flowers and seeds are bigger and energetically more costly than those of CL. Although the effects of inbreeding and floral dimorphism are critical to understanding the evolution and maintenance of cleistogamy, these effects have been repeatedly confounded. In an attempt to separate these effects, we compared the performance of progeny derived from the two floral morphs while controlling for the source of pollen. That is, flower type and pollen source effects were assessed by comparing the performance of progeny derived from selfed CH vs. CL and outcrossed CH vs. selfed CH flowers, respectively. The experiment was carried out with the herb Ruellia nudiflora under two contrasting light environments. Outcrossed progeny generally performed better than selfed progeny. However, inbreeding depression ranges from low (1%) to moderate (36%), with the greatest value detected under shaded conditions when cumulative fitness was used. Although flower type generally had less of an effect on progeny performance than pollen source did, the progeny derived from selfed CH flowers largely outperformed the progeny from CL flowers, but only under shaded conditions and when cumulative fitness was taken into account. On the other hand, the source of pollen and flower type influenced seed predation, with selfed CH progeny the most heavily attacked by predators. Therefore, the effects of pollen source and flower type are environment-dependant and seed predators may increase the genetic differences between progeny derived from CH and CL flowers. Inbreeding depression alone cannot account for the maintenance of a mixed mating system in R. nudiflora and other unidentified mechanisms must thus be involved.
Assuntos
Acanthaceae/fisiologia , Flores/fisiologia , Aptidão Genética/fisiologia , Polinização/fisiologia , Autofertilização/fisiologia , Acanthaceae/parasitologia , Animais , Evolução Biológica , Meio Ambiente , Comportamento Alimentar/fisiologia , Flores/anatomia & histologia , Flores/parasitologia , Endogamia , Luz , México , Mariposas/fisiologia , Pólen/fisiologia , Comportamento Predatório/fisiologia , Reprodução , Sementes/parasitologiaRESUMO
Few studies have simultaneously addressed the effects of biotic and abiotic factors on pre-dispersal seed predation (PSP). Plant-seed predator interactions may be influenced by natural enemies and pollinators (the latter through changes in fruit or seed traits), and the activity of pre-dispersal seed predators and their natural enemies may both be affected by the abiotic environment. Additionally, in the case of cleistogamous plants with fruit dimorphism, PSP may be biased towards larger and more seeded chasmogamous (CH) fruits [relative to the smaller cleistogamous (CL) fruits], and the effects of biotic and abiotic factors may be contingent upon this fruit dimorphism. We studied PSP in the cleistogamous Ruellia nudiflora using a split-plot experimental design and asked the following: (1) is PSP biased towards CH fruits and is there an effect of pollen load on PSP? (2) Do parasitoids influence PSP and is their effect influenced by pollen load or fruit type? And (3) do light and water availability modify PSP and parasitoid effects? PSP was higher for CH relative to CL fruits, and under low water availability it was lower for pollen-supplemented CH fruits relative to open-pollinated CH fruits. Parasitoids were not influenced by abiotic conditions, but their negative effect on PSP was stronger for pollen-supplemented CH fruits. Overall, we show that fruit dimorphism, abiotic factors and natural enemies affect PSP, and that these effects can be non-additive.
Assuntos
Acanthaceae/fisiologia , Ecossistema , Frutas/fisiologia , Sementes/citologia , Acanthaceae/parasitologia , Frutas/anatomia & histologia , Frutas/parasitologia , Modelos Lineares , México , Polinização/fisiologia , Reprodução , Dispersão de SementesRESUMO
BACKGROUND AND AIMS: Mixed reproductive strategies may have evolved as a response of plants to cope with environmental variation. One example of a mixed reproductive strategy is dimorphic cleistogamy, where a single plant produces closed, obligately self-pollinated (CL) flowers and open, potentially outcrossed (CH) flowers. Frequently, optimal environmental conditions favour production of more costly CH structures whilst economical and reliable CL structures are produced under less favourable conditions. In this study we explore (1) the effect of light and water on the reproductive phenology and (2) the effect of pollen supplementation on resource allocation to seeds in the cleistogamous weed Ruellia nudiflora. METHODS: Split-plot field experiments were carried out to assess the effect of shade (two levels: ambient light vs. a reduction of 50 %) and watering (two levels: non-watered vs. watered) on the onset, end and duration of the production of three reproductive structures: CH flowers, CH fruit and CL fruit. We also looked at the effect of these environmental factors on biomass allocation to seeds (seed weight) from obligately self-pollinated flowers (CL), open-pollinated CH flowers and pollen-supplemented CH flowers. KEY RESULTS: CH structures were produced for a briefer period and ended earlier under shaded conditions. These conditions also resulted in an earlier production of CL fruit. Shaded conditions also produced greater biomass allocation to CH seeds receiving extra pollen. CONCLUSIONS: Sub-optimal (shaded) conditions resulted in a briefer production period of CH structures whilst these same conditions resulted in an earlier production of CL structures. However, under sub-optimal conditions, plants also allocated more resources to seeds sired from CH flowers receiving large pollen loads. Earlier production of reproductive structures and relatively larger seed might improve subsequent success of CL and pollen-supplemented CH seeds, respectively.