Pablo Ortega-Baes

Global diversity and conservation priorities in the Cactaceae

The purpose of this paper was to analyze the diversity patterns of Cactaceae at a global scale, to identify those countries where conservation actions should be performed. In order to do this, the species richness and the number of endemic species for 34 American countries were determined. With these data, the relationship between the total number of species or the number of endemic species and the area of the countries were analyzed. In addition, a complementarity analysis was conducted to determine the most important countries for cactus conservation. Results showed that Mexico had the highest number of total and endemic species followed by Argentina, Bolivia, Brazil, and Peru, among others. There was a significant positive relationship between both, the total and endemic species, and the area of the countries. Despite this fact, the cactus diversity in Mexico, Argentina, Peru, Bolivia, Chile, and Costa Rica was higher than expected according to their area. Further, these countries also presented the highest proportions of endemic species. The complementarity analysis indicated that 24 countries are necessary to preserve all cactus species. However, 94% of all species could be preserved with only 10 countries. Considering the diversity patterns and the complementarity analysis, three important groups for cactus conservation were identified: (1) Mexico, Argentina, Peru, Bolivia, Chile, and Costa Rica, (2) Paraguay and Cuba, and (3) Brazil and USA. Conservation efforts should be focused on these countries in order to preserve cactus diversity.

Diversity and Conservation in the Cactus Family

Cacti are conspicuous elements of the Western hemisphere. They have long attracted attention due to their peculiar biology, and have maintained close relationships with local settlers. Cacti are used as food, fodder, medicinal and ornamental plants, and as a source of wood. The greatest diversity of this family is recorded in Mexico, with 586 species, followed by Brazil, Argentina, Bolivia and Peru. These countries are also the richest in endemic species. The underlying factors affecting diversity patterns are varied and include temperature, rainfall and geological history. Cacti are threatened by loss and degradation of habitat, and illegal collection. Though it is commonly stated that many species are endangered, most have not yet been evaluated. Due to the growing impact of human activities on biodiversity it is necessary to increase conservation actions to preserve this interesting group of plants, especially in South American countries where knowledge and conservation of cacti are still incipient.

Fire responses of three co-occurring Asteraceae shrubs in a temperate savanna in South America

South American temperate savannas have undergone significant woody plant encroachment through changes in their disturbance regimes. We studied fire strategies and the spatial variation in individual fire responses of Eupatorium buniifolium, Baccharis medullosa and B.xa0dracunculifolia, the dominant shrub species at El Palmar National Park, in areas with different fire history. In recently burnt sites, all Baccharis dracunculifolia individuals died, whereas all E.xa0buniifolium and B.xa0medullosa individuals sprouted. The relative growth rate was higher in E.xa0buniifolium, which invested more biomass in shoots, and in B.xa0medullosa, which invested more biomass in leaves. At the unburnt site, B.xa0dracunculifolia showed the highest growth rate and leaf biomass. B.xa0medullosa produced capitula immediately after fire, whereas E.xa0buniifolium reproduction was delayed for 1xa0year. In both species, production of capitula and reproductive effort were higher in recently burnt sites. For B.xa0dracunculifolia, production of capitula was lower and the reproductive effort was higher in burnt than in unburnt sites. Seedling establishment was extremely low for E.xa0buniifolium, low for B.xa0medullosa and high for B.xa0dracunculifolia in both recently burnt sites. E.xa0buniifolium behaved as a sprouter, B.xa0medullosa as facultative sprouter and B.xa0dracunculifolia as obligate seeder species. In order to control the increase and/or attain desirable population levels of these species, fire management practices in these savannas should consider individual species’ responses, particularly to the time since the last fire.

Conservation priorities in the Southern Central Andes: mismatch between endemism and diversity hotspots in the regional flora

North western Argentina, the southernmost portion of the tropical Andes, contains one of the main areas of endemism within the Southern Cone, as well as one of the main diversity hotspots of the country. Historically its reserve area systems have been located in the richest ecoregion of the area; the Southern Andean Yungas. We evaluated the effectiveness of the current protected areas in preserving the endemic flora of the region. The distributions of 505 endemic species were either modeled or included as observed data to determine endemism hotspots in each ecoregion. The endemic species were mainly found in arid ecoregions such as the High Monte and the Central Andean Puna, as well as in the transition zones between these regions and the Southern Andean Yungas. We found that more than 1/3 of the endemic species are unprotected in their entire ranges by the current system, while nearly half of the species are protected in only 5xa0% of their distribution ranges. New priority areas were chosen to increase the effectiveness based on the irreplaceability concept. We show that adding 251 new cells of 100xa0km2 each would improve the protection values and convert the system to effective. The present paper highlights that priorities set on the basis of species richness may not successfully conserve areas of high plant endemism. However, zoologist would have to realize similar assessments in the endemic fauna in order to find the optimal designed of protected areas system to conserve both the endemic flora and fauna in the Southern Central Andes.

Spatial patterns of dicot diversity in Argentina

In this paper, we analyzed the taxonomic diversity of the Argentine dicots to evaluate their relationships with area, latitude, and longitude. We also evaluated species diversity and higher taxa diversity relationships. The families, genera and species diversity in Argentine dicots was not explained by the area of each province but it varied through latitudinal and longitudinal gradients. The taxonomic diversity of these plants increased from high to low latitudes and west–east longitudes. These patterns would explain why the main diversity centers are located in the North region of this country. As we expected the species diversity and higher taxa diversity showed a positive relationship. At this scale, higher taxa diversity could be use as surrogate for species diversity.

The explosive pollination mechanism in Papilionoideae (Leguminosae): an analysis with three Desmodium species

In the papilionaceous flowers with explosive pollination mechanism, the androecium and the gynoecium are subjected to great pressure in the keel. It has been suggested that at the first visit nearly all pollen grains are released and that the floral parts do not return to their original positions; this would be a cue for pollinators to avoid activated flowers. The dependence on the pollinators suggests that explosive flowers will not produce fruits if the mechanism is not activated. In this paper, we have tested these ideas studying the reproductive biology of three Desmodium species, D. incanum, D. subsericium and D. uncinatum. Specifically, we studied the floral traits, reproductive system, pollination mechanism and floral visitors, for the three species. The results indicated that the keel and the wings play a key role in the activation of the explosive mechanism. The three species have a secondary pollen presentation, diurnal flowers, and a short floral cycle. According to the results, all the species studied were self-compatible, with two species producing fruits by autonomous self-pollination. Desmodium flowers were visited and activated by native and exotic bee species. During the first visit nearly all the pollen was released; after that, new visits were low or null. Our results indicated that the activation of the mechanism is not essential for the production of fruits, that explosive flowers are visited only once and that the changes in the positions of the floral parts are the cues that keep pollinators away from the flowers with activated mechanism.

Tropical high Andean drylands: species diversity and its environmental determinants in the Central Andes

Diversity determinants have mostly been evaluated in high diversity areas, leaving behind regions with less species diversity such as drylands. Here we aim to analyze the patterns of plant diversity in tropical drylands in the southern Central Andes, and determine the importance of water, energy, and environmental heterogeneity as diversity determinants of the arid and semi-arid adapted flora. We examined the distribution of 645 native species from lowlands to 6000xa0m.a.s.l. in the north-western region of Argentina (NWA) and define hotspots of diversity within each NWA ecoregion. Diversity is concentrated in regions of middle elevation with intermediate values of water and energy, at the transition between arid and semi-arid regions. Furthermore, we showed that in tropical drylands energy input is as fundamental for plant diversity as water input is and, we found that the effects of these variables varied with elevation and, also with aridity. Water variables had the strongest effect on the flora in the arid high Andean ecoregions, where an increase in precipitation during the growing season stimulated species diversity. Energy only became more important than water when the arid adapted flora entered the low and semi-arid regions where energy increments reduce species diversity. Our analysis provides strong quantitative support for climate variables as the main determinants of plant diversity across different ecoregions of the southern Central Andes. Given the present climate change events, knowing how these variables affect the distribution of the arid adapted flora is crucial for planning strategies for achieve their present and future conservation.