Effect of light on germination of seven species of cacti from the Zapotitlán Valley in Puebla, México

Seed germination of seven species of cacti from Zapotitlán Valley, Puebla, Mexico, were compared at four different light treatments (red light, far-red light, white light and darkness) at a constant temperature of 25°C, and at two light treatments (white light and darkness) at two fluctuating temperatures (15–30°C and 20–30°C). Results allowed us to divide the studied species into two groups: positive photoblastic and indifferent to light. Positive photoblastics were barrel cacti and indifferent to light species were columnar cacti. Although barrel cacti had a light requirement for germination, they germinated in far-red light. Probable relationships among life-form, species distribution and light requirements for germination are discussed.     

Gendered production spaces and crop varietal selection: Case study in Yucatán, Mexico

This paper examines the influence of gender relations and gendered domains on maize and squash varietal selection in a village in Yucatán State, southeast Mexico. Results of the exploratory study indicate that the traditional production spaces of homegardens and agricultural fields are complementary gendered domains of varietal maintenance for both crops although with different cropping patterns, while a 'new' space, of land allocated to some families for future residential construction ( terreno ) is in the meantime a jointly worked agricultural domain. Women's labour, knowledge and preferences predominate in post-harvest processes. Fieldwork revealed that neither men nor women are independent decision-makers, planning what to grow, where and in what amounts, but that in most aspects of farming the interests of both are accommodated within the household's production spaces.     

Soil seed flora, germination and regeneration pattern of woody species in an Acacia woodland of the Rift Valley in Ethiopia

The objectives of this study were to determine the composition, density and spatial distribution of the soil seed bank of woody species, as well as their regeneration pattern in two different land use systems, controlled (ranch) and open grazing, in an Acacia woodland of the Rift Valley in Ethiopia. We also compared the species composition of the soil seed bank and the above-ground vegetation to find out if differences exist in the soil seed bank and advance regeneration between the two land use systems. The germination requirements of seeds of the woody species were also investigated under laboratory conditions. Acacia senegal, Acacia seyal, Acacia tortilis, Dichrostacys cinerea and Balanites aegyptiaca were encountered in the above-ground vegetation in both systems. Seeds of only A. tortilis (90±32 seeds m⁻²) from the ranch, and A. senegal (5±3 seeds m⁻²) and A. tortilis (72±34 seeds m⁻²) from the open system were found in the soil seed bank along transects with patchy horizontal pattern. The two systems were not significantly different in density of soil seed banks of A. senegal andA. tortilis . Jaccard's similarity index showed that only a few woody species were common in the soil seed flora and above ground vegetation. However, all of the species accumulated seeds (58±43–331±130 seeds m⁻²) in/on the soil under the canopy. Very large numbers of seeds of A. tortilis (19382±9722 seeds m⁻²) and D. cinerea (1278±494 seeds m⁻²) were also found in barns. Most of the seeds recovered from the soil samples (60–80%) were found in the litter layer. Acid and mechanical scarification improved legume germination (36–99% and 60–99%, respectively) over boiling water (0–48%). Treatment means differed significantly for all the legumes (p<0·001) but not for Balanites. Height and diameter class distribution of regeneration of A. tortilis and D. cinerea in both systems and A. senegal in the open system had a negative exponential correlation (r_s=−0·5, −0·25 and −0·86, respectively). A. seyal and B. aegyptiaca showed poor regeneration. Horizontal distribution of advance regeneration of all the species was patchy. Advance regeneration of A. seyal, A. tortilis and B. aegyptiaca were not significantly different, while that of A. senegal and D. cinerea were significantly different between the two systems. Poor representation of species in the soil seed bank along transects and in the different height and diameter classes may be attributed to the low density of mature trees as well as the mode and strategy of seed dispersal. Ungulate and wind dispersed species (e.g. A. senegal, A. tortilis and D. cinerea) were highly favoured. Patchiness in the distribution of seeds and advance regeneration was also a result of endozoochory. Dispersal of non-ungulate dispersed seeds (A. senegal, A. seyal and B. aegyptiaca) was restricted to the canopy zone. Piles of seeds ofA. tortilis and D. cinerea that were found in barns were a result of consumption of their pods by cattle. High concentration of seeds in the litter layer may be due to low soil disturbance and larger size of seeds. The height and diameter class distribution of A. senegal (in the open system), A. tortilis and D. cinerea also indicated that the species have good regeneration. Results from the germination tests indicated that seeds of the legumes require pre-sowing treatments to give a rapid, uniform and improved germination. Intervention through artificial regeneration should be employed to improve the density and regeneration capacity of those species with hampered regeneration at both systems.     

Building participatory landscape-based conservation alternatives: A case study of Michoacán, Mexico

Michoacán, as one of the most species-rich provinces of Mexico and with high levels of endemism, was used for testing the potential of a conservation approach based on biodiversity as determined by scientists and local stakeholder's preferences. The resulting zones covered over 17% of the area of Michoacán in 18 zones. As a result of this study the first “large” tropical dry forest biosphere reserve in Mexico is currently being established. In conclusion, landscape-based conservation zoning based on local stakeholders' perspectives as well as on critical biodiversity indicators, proved to be effective for achieving science-based and politically acceptable nature conservation schemes.     

Reproductive and recruitment traits as indicators of the invasive potential of Kalanchoe daigremontiana (Crassulaceae) and Stapelia gigantea (Apocynaceae) in a Neotropical arid zone

Populations of two ornamental exotic species, Kalanchoe daigremontiana and Stapelia gigantea, have been recently detected inside a protected area containing arid ecosystems in Venezuela. We indirectly tested their invasive potential by characterizing their reproductive biology and recruitment patterns and comparing our estimates against Baker's Law and reproductive profiles reported for invasive plants. K. daigremontiana is autogamous, produces >16,000 seeds per plant and also reproduces clonally. Despite low seed viability (17.9%) and germination rates (11.9%), seeds were present in the seed bank. Plantlets of asexual origin showed high survival (75–100%) compared to seedlings of sexual origin (10%). S. gigantea is self-incompatible, xenogamous and produces close to 1500 seeds per m² of plant tissue. Seed viability (77%) and germination rates (62%) were high, but this species is not represented in the seed bank. It has a vegetative growth. A combination of reproductive and recruitment attributes, which match those considered in Baker's Law and others reported for invasive plants, confer K. daigremontiana and S. gigantea the potential to invade Neotropical arid zones; the former mainly through selfing and production of numerous asexual plantlets, and the latter through an association with a locally abundant pollinator and production of wind dispersed seeds.     

Factors affecting the distribution, abundance and seedling survival of Mammillaria gaumeri , an endemic cactus of coastal Yucatán, México

The population status of an endemic cactus (Mammillaria gaumeri) was assessed in coastal Yucatán, México. Similar numbers of mature plants were found in open and full sun microhabitats. Plants in full sun had more ramets and were of larger diameter. There was a correlation between M. gaumeri abundance and the biomass of a disturbance indicator, Myrmecophila tibicinis (Orchidacea). Higher seedling survival in shade microhabitats and aggregated distribution of adults suggests that shrubs serve as nurse plants. Initial mortality rates of seedlings were many times higher in full sun microhabitats than in shade conditions. Herbivory had no effect on seedling survival.     

Effects of seed age and seeding depth on growth of Stipa lagascae R. & Sch. seedlings

Native grass species are being considered in the restoration of degraded rangelands in Tunisia due to the failure of introduced species to adapt to the ecological constraints of the region. The objective of this study was to determine the effects of seed age and seedling depth on emergence and seedling vigor of Stipa lagascae, a perennial bunchgrass that is native to the region and shows promise as a species for restoration purposes. Total emergence percentage of seedlings and the coefficient of rate of emergence (CRE), the seedling vigour as well as above and below-ground biomass were measured. Younger seeds had higher emergence rates than older seeds. However, seed age did not affect variables associated with seedling vigour. Seeding depth significantly affected all parameters tested. A seeding depth of 4–6 cm was found to be optimal.     

Seed predation and moisture limit germination of recalcitrant Dobera glabra (Salvadoraceae) seeds in the Afar rangelands, Ethiopia

We studied current recruitment failure of Dobera glabra, an important famine-food throughout the dryland parts of the Horn of Africa. The species has previously been found to have recalcitrant seeds, a strategy not common for plants in dryland areas. We experimentally tested (1) how germination capacity of D. glabra is affected by seed form, storage period and moisture under nursery conditions, and (2) how seed predation by vertebrate herbivore and seed exposure at germination site affect germination under field conditions in northern Afar rangelands, Ethiopia. D. glabra seeds that received either mulching or supplementary watering (3 days/week) had a higher germination success than controls. The seeds are probably desiccation sensitive since stored seeds had poor germination performance compared to fresh seeds. Seeds in the rangeland plots protected from herbivores had significantly higher germination success compared to open plots. Our findings demonstrate that seed predation and moisture limitation highly reduced the germinability of the recalcitrant D. glabra seeds, indicating that the species might have persisted due to past wetter periods and low herbivore density in dry environments.     

The ecology of Lerista labialis (Scincidae) in the Simpson Desert: reproduction and diet

This study investigated the diet and reproductive cycle of the southern sandslider skink Lerista labialis, in the dunefields of the Simpson Desert, central Australia. We dissected preserved specimens to obtain gut contents and measure gonad volume, and also live-captured animals from 1999 to 2000 to assess the impact of rainfall on population structure and body condition. This skink breeds during the austral summer. Males start spermatogenesis in July and testes volume is largest in December. Females have enlarged ovarian follicles in November and produce oviducal eggs from November to February. One or more clutches of two eggs are produced per breeding season. L. labialis specializes on termites, which represent 78% of the diet by percentage occurrence. The remaining 22% of this skink's diet comprises Hemiptera, Neuroptera and unknown prey items. Body condition, and probably increased reproduction and juvenile survival, were higher in 2000 (wet year) than 1999 (relatively dry year); proportion of juveniles also increased in the population in autumn, winter and summer 2000 compared to the previous year. Late rainfall in autumn 2000 may have triggered these demographic changes by increasing prey accessibility. Long-term research is required into growth rates, longevity and inter-annual population dynamics of L. labialis to fully evaluate its life history strategy.     

Differences in production and mortality of reproductive structures in two Prosopis L. (Mimosaceae) shrub species from Patagonia, Argentina

Prosopis L. pods have been proposed as a source of gum (galactomannans), with potential applications as a thickening agent in the food industry. The objective of this work was to compare, under field conditions, the production and mortality of reproductive structures in two sympatric shrub species of Prosopis: P. alpataco Phillipi and P. denudans Bentham. Our results indicate that fruit production in Prosopis denudans and P. alpataco is very low and erratic in non-irrigated lands. Although large quantities of flowers (15,000–25,000 flowers*0.40 m⁻²) can be found in one flowering season, 70–80% are shed before they reach anthesis and 20–28% are aborted between anthesis and fruit set. We conclude that the utilization of native populations of Prosopis denudans and P. alpataco for fruit production in Patagonian steppe, could not guarantee a consistent supply for the food industry.     

Spatial and temporal distribution of tenebrionid species (Coleoptera) in the Negev Highlands, Israel

Tenebrionid species composition and activity level were studied, using pitfall traps, in two sandy (dune and stabilized sand field) and four compact soil (wadi, north- and south-facing slopes, and loess plain) habitats in the Negev Desert Highlands, Israel. Each soil type had a distinctive species composition but habitats within soft types were similar both in species composition and phenologies. The number of species was not correlated with habitat primary production; it was low in sandy habitats (19 spp.) and high in compact soil (33 spp.) habitats. Within the compact soil habitats, large-size species were abundant only in the high plant-cover wadi, and the low plant-cover slopes and plain were dominated by smaller species. We suggest that low plant cover on the slopes and plain exposes large tenebrionids to predation by birds and limits them to the wadi where they are concealed and find refuge in the plant cover.     

Sediment and Water Discharge Assessment on Santiago and Pánuco Rivers (Central Mexico): The Importance of Topographic and Climatic Factors

This study explores the main factors controlling sediment and water discharge in the Santiago and Pánuco Rivers, the two largest rivers of central Mexico. Both Santiago and Pánuco Rivers are sourced in the Central Plateau of Mexico and flow in an opposite direction. Santiago River flows over a tectonically active margin draining to the Pacific Ocean, and Pánuco River flows into the passive margin of the Gulf of Mexico. Mean annual and monthly values of suspended sediment load and water discharge spanning around 50 years were used to evaluate sediment load and water discharge in these two rivers. Our findings indicated that Santiago River delivers to the ocean around 45% more sediment than Pánuco River. However, we found that Santiago River has about half the water discharge of Pánuco River. The high river gradient along Santiago River is likely to enhance the net erosion and sediment transport capacity. Water discharge at Pánuco Basin is higher than in Santiago Basin because the annual rainfall is higher for the former. The difference in sediment and water discharge for both rivers are also related to El Niño Southern Oscillation events. Our results indicated that water discharge in Santiago River increases during El Niño and La Niña events. In contrast, Pánuco River is mostly affected by La Niña events.     

Land use/cover, landforms and fragmentation patterns in a tropical dry forest in the southern Pacific region of Mexico

In spite of widely documented studies of deforestation rates and land use/cover changes in tropical dry forests in Mexico, relatively little is known about fragmentation patterns in such forests. This study defines the spatial distribution of landforms and land use/cover types the lower Papagayo River basin and examines their influence on fragmentation patterns and biological diversity in a tropical dry forest in that southern Pacific region. The land use/cover map was constructed from aerial photographs, Landsat TM imagery (2000) and fieldwork. Landform units were defined based on altitude, slope, lithology and morphology. Landscape fragmentation parameters were obtained using FRAGSTATS (version 3.3) considering the numbers of patches, mean, minimum and maximum patch size, edge density, total edge and connectivity. Results show tropical dry forest to be remnant vegetation (~11 per cent), characterized by isolation and low connectivity. Land use/cover types have different effects on fragmentation patterns. Agriculture and cattle raising produce similar numbers of patches, but with a different mean size; and human settlements have a scattered distribution pattern. The abandonment of rural agricultural livelihoods has favoured the expansion of secondary tropical dry forest characterized by continuity and high connectivity, which suggests a high regeneration potential from land abandonment. It can be concluded that tropical dry forest fragmentation and recovery at regional scales depend on such landscape attributes as lithology, slope, geomorphology and management.     

Research strategies for the improvement of cactuspear (Opuntia ficus-indica) fruit quality and production

Cactus pear (Opuntia ficus-indica L.) is cultivated worldwide for fruit production either in the subsistence agriculture of dryland areas or as a cash crop. However, little horticultural research has been devoted to this species so far. Research needs related to reproductive biology as well as productivity and orchard management are outlined. A better knowledge of the environmental influence on reproductive biology and fruit quality, the control of fluctuations in plant cropping, as well as the reduction of seed number and size, are the major challenges for future research. Cactus pear will transcend the ethnical markets only if adequate marketing strategies can be promoted and fruit quality enhanced and standardized.     

Soil physico-chemical properties affecting the distribution of biological soil crusts along an environmental transect at Zapotitlán drylands, Mexico

The composition of cyanobacteria, mosses, and lichens of biological soil crusts were correlated with soil characteristics and sun exposure along an environmental transect. The study was conducted in Zapotitlán drylands, a locality within the Tehuacán–Cuicatlán Valley, central Mexico, where a great variety of environments for crust development exist due to landscape fragmentation. Data were analyzed with redundancy and Sorensen analysis. Soil crusts consisted of different combinations of cyanobacteria (7 species), mosses (19 species), and lichens (8 species). The relative frequencies of these groups were positively correlated with soil apparent density and lichens were also positively correlated with soil pH. However, there were no significant correlations with sun exposure.     

Effect of rhizobia inoculation on the seed (herbage) production of mungbean (Phaseolus aureusRoxb.) grown at Uzbekistan

In field trials conducted at Uzbekistan, inoculation of mungbean (Phaseolus aureusRoxb.) with commercial strain CIAM1901 ofBradyrhizobiumsp. (Phaseolus) increased (on average for two cultivars) the herbage mass by 46·6±6·0%, seed mass by 39·2 ± 3·6%, mass of 1000 seeds by 16·0 ± 0·8%, nitrogen content in seeds by 58·3 ± 8·9%, starch content in seeds by 30·0 ± 5·5% and number of nodules by 254%. Inoculation with this strain produced the same herbage (seed) mass as NH₄NO₃application (120 kg ha⁻¹of N), while the combined treatment of rhizobia and 60 kg ha⁻¹of N produced significantly higher yields than rhizobia inoculation alone or application of 120 kg ha⁻¹of N. The rhizobia strain M11 was isolated from Uzbekistan soils and significantly exceeded the commercial strain CIAM1901 in its influence on herbage mass by 3·9–10·6%. Two-factor analysis of variance demonstrated that the herbage mass and number of nodules are controlled mainly by the rhizobia strain genotypes, while seed yield, number of pods, mass of 1000 seeds and N and starch content in seeds are influenced by the plant cultivar genotypes.     

Adaptation to living in an open arid environment: lessons from the burrow structure of the two southern African whistling rats, Parotomys brantsii and P. littledalei

This study examines interspecific differences in the architecture and field characteristics of the burrow systems of Brants' whistling rat, Parotomys brantsii, and Littledale's whistling rat, Parotomys littledalei. The two rodents are endemic to the arid west region of southern Africa. Both build complex burrow systems with numerous nest chambers and associated interconnecting tunnels, as well as a number of entrances. Burrow systems of P. littledalei are restricted to areas of good plant cover, whilst many P. brantsii burrows are situated in open locations with only limited plant cover. Further, the burrows of P. brantsii cover a much larger area than those of P. littledalei, with many more entrances. As P. brantsii feed predominantly within the boundaries of their burrows and not in the open veld, their burrow systems effectively serve as a predator refuge, into which this diurnal rodent can quickly run in the event of danger. Thus, by building large multi-holed burrow systems, P. brantsii have become independent of the protection offered by bush cover and can exist within relatively open areas within their distributional range. On the other hand, the reduced number of entrances to P. littledalei burrow systems may largely restrict this species to areas with adequate cover, including coastal and riverine bush, with which it is often associated.     

Local- and watershed-scale controls on the spatial variability of natural levee deposits in a large fine-grained floodplain: Lower Pánuco Basin, Mexico

This study examines spatial variations in natural levee deposits within the lower reaches of a large coastal plain drainage system. The Pánuco basin (98,227 km²) drains east-central Mexico, and is an excellent setting to examine the influence of watershed and local controls on the morphology and sedimentology of natural levees. Although many fluvial systems in the U.S. Gulf Coastal Plain have been investigated, the rivers in the Mexican Gulf Coastal Plain have received comparatively little attention. Lateral and downstream characteristics of natural levee morphology and sediment texture are considered within the context of meandering river floodplain deposits. Data sources include total-stations surveying, sediment samples of surficial levee deposits, topographic maps (1:50,000), and aerial photographs (1:40,000). The slope of natural levees average 0.0049 m/m, whereas the texture (D₈₄) of levee deposits averages 0.12 mm. Natural levee characteristics vary due to local- and watershed-scale controls. The lateral reduction in levee height displays a curvilinear pattern that coincides with an abrupt change in sediment texture. The downstream pattern of natural levee texture exhibits the influence of local-scale perturbations superimposed upon a larger watershed-scale trend. Disruption to the fining trend, either by tributary inputs of sediment or reworking of Tertiary valley deposits, is retained for a limited distance. The influence of the channel planform geometry on levee morphology is examined by consideration of the radius of curvature (R_c) of meander bends, and is inversely related to natural levee width. This suggests that the planform geometry of river channels exerts a control on the dispersal of flood sediments, and is responsible for considerable local variability in the floodplain topography. The average width of natural levees increases with drainage area, from an average of 747 m in the Moctezuma to an average of 894 m in the Pánuco. However, in the lower reaches of the Pánuco valley the width of natural levees rapidly decreases, which is associated with fining of the suspended sediment load. Thus, the reduction in natural levee width signifies an abrupt change in the directionality of cause–effect relationships at the watershed-scale. Findings from this study elucidate linkages between meandering river channels and floodplains for a large lowland alluvial valley.     

Paleoshoreline geomorphology of Böön Tsagaan Nuur, Tsagaan Nuur and Orog Nuur: the Valley of Lakes, Mongolia

We conducted a preliminary study of paleoshoreline features associated with Böön Tsagaan Nuur, Tsagaan Nuur, and Orog Nuur, lakes located in the Gobi–Altai transition zone of the Valley of Lakes (Dolina Ozor) which stretches from central to western Mongolia. The paleoshoreline features were first identified on RADARSAT satellite SAR imagery. We investigated the features during the 1998 field season of the Joint Mongolian–Russian–American Archaeological Expedition to the Gobi–Altai region. We identified paleoshorelines of multiple elevations in the field, which are considered to be relict beach ridges and wave-cut terraces. Other paleolake landforms include spits and Gilbert-type deltas. These landforms are complex, large and well established, implying that the paleolakes were stable for extended periods. The reconstructed paleolakes cover extensive areas of the valley floor, implying that hydrological and climatic conditions were very different in the past. Paleolake expansions may have occurred under a variety of circumstances. One hypothesis is that the high lake stands occurred during the wetter period corresponding to the Oxygen Isotope Stage 3 prior to the Last Glacial Maximum (LGM), during the warmest early Holocene and the late Holocene, or during all these periods. If low evaporation rates due to lower temperatures, glacier meltwater and possibly increased precipitation are important factors, then the expansions may have occurred during the terminal Late Glacial period after the Last Glacial Maximum. The greatly expanded lakes in the Gobi–Altai could have significantly affected the Quaternary human demography and migration in the region.