Heidi Romero-Schmidt

Observations on distribution and habitat characteristics of the endangered Mexican endemic cacti Stenocereus eruca

Abstract Six 100 × 100m quadrants were established in the arid area where Stenocereus eruca has been recorded, all individuals were counted and measured and the main habitat characteristics recorded. A new distribution record is reported, but these observations indicate that the original range is threatened. It is recommended that the establishment of a reserve in the northern part of the range where habitat characteristics promote locally abundant populations and thus implement a genetic reservoir in order to guarantee the conservation of this unique endemic cacti.

Changes in lizard abundance on protected versus grazed desert scrub in Baja California Sur, Mexico

The changes in abundance of three species of lizards were determined and compared between grazed and ungrazed desert scrub near La Paz, in the Cape Region, Baja California Sur, Mexico, from April 1992 to March 1993. A total of 54 censuses were taken of these species over two transect systems, one inside and one outside livestock enclosure. Urosaurus nigricaudus were negatively affected by the grazing activities, but Uta stansburiana exhibited an apparently positive effect by such activities. Cnemidophorus hyperythrus population apparently showed no effect by the livestock grazing. The paper discusses the possible relationship between the microhabitat specificity of each species and their population number individuals response.

Livestock exclusion: consequences on nocturnal rodents in Baja California Sur

Inflorescences of Baclris gasipaes (a moooecioos neolropica1 pahn) present a strong prezigotic resource allocation toward masculinity on the inflorescence. Male reproductive effort (ERM. biomass) was 0.82 ± 0.11 g male flowers / g inflorescence. A high conelatioo between me total inflorescence biomass with female reproductive effort (ERF) (r= 0.76), indicates that plants wim bigger inflorescences allocate more resources to ihe female functioos. The pistillate flowers are situated preferentially in me inner pans of rachillas. Early ideas about evolution of protoginy, resource allocation and plant sexual systems are supported by these data.