Vulnerability of the northern Mongolian steppe to climate change: insights from flower production and phenology

The semiarid, northern Mongolian steppe, which still supports pastoral nomads who have used the steppe for millennia, has experienced an average 1.7 degrees C temperature rise over the past 40 years. Continuing climate change is likely to affect flowering phenology and flower numbers with potentially important consequences for plant community composition, ecosystem services, and herder livelihoods. Over the growing seasons of 2009 and 2010, we examined flowering responses to climate manipulation using open-top passive warming chambers (OTCs) at two locations on a south-facing slope: one on the moister, cooler lower slope and the other on the drier, warmer upper slope, where a watering treatment was added in a factorial design with warming. Canonical analysis of principal coordinates (CAP) revealed that OTCs reduced flower production and delayed peak flowering in graminoids as a whole but only affected forbs on the upper slope, where peak flowering was also delayed. OTCs affected flowering phenology in seven of eight species, which were examined individually, either by altering the time of peak flowering and/or the onset and/or cessation of flowering, as revealed by survival analysis. In 2010, which was the drier year, OTCs reduced flower production in two grasses but increased production in an annual forb found only on the upper slope. The particular effects of OTCs on phenology, and whether they caused an extension or contraction of the flowering season, differed among species, and often depended on year, or slope, or watering treatment; however, a relatively strong pattern emerged for 2010 when four species showed a contraction of the flowering season in OTCs. Watering increased flower production in two species in 2010, but slope location more often affected flowering phenology than did watering. Our results show the importance of taking landscape-scale variation into account in climate change studies and also contrasted with those of several studies set in cold, but wetter systems, where warming often causes greater or accelerated flower production. In cold, water-limited systems like the Mongolian steppe, warming may reduce flower numbers or the length of the flowering season by adding to water stress more than it relieves cold stress.     

Occurrence and reproductive success of feminized males in the polychaete Capitella capitata (Species Type I)

Natural populations of the cosmopolitan polychaete species, Capitella capitata (Species Type I, Grassle and Grassle 1976) contain males, females and hermaphrodites. Hermaphroditic individuals arise through feminization of males when females are rare. The age-specific survivorships and fecundities of females and hermaphrodites were estimated. There were no significant differences between females and hermaphrodites in survivorship, number of offspring per brood, or percentage of aborted eggs per brood. Net reproductive rates were used to estimate fitness, and the relative fitness of a hermaphrodite as a female ranged from 0.09 to 0.31. The fitness differential was due to the difference in the number of broods that females and hermaphrodites produce. The effects of density, sex ratio, age and body size on the timing of the development of hermaphrodites in groups of siblings were also examined. Hermaphrodites appeared when females were rare or when densities were low. Hermaphrodites never developed in cohorts with larger males unless females were rare. These observations suggest that feminization of males occurs when some males are unable to gain access to females because of mate competition. Feminization does not appear to be correlated with a threshold in body size.