The More the Scarier: Adult Richardson's Ground Squirrels (Spermophilus richardsonii) Assess Response Urgency Via the Number of Alarm Signallers

Richardson’s ground squirrels (RGS) produce alarm calls that warn conspecifics of potential predators. We presented free‐living adult and juvenile RGS with playbacks of repetitive alarm calls from one vs. two juvenile callers broadcast sequentially through two spatially separated loudspeakers. Adult RGS spent a greater proportion of time vigilant in response to two vs. one calling squirrel, whereas juvenile RGS did not respond differentially to two vs. one caller. Apparently then, the relative inexperience of juvenile RGS with alarm calls and the context in which such calls are emitted precludes their enumeration of alarm callers. Taken together with our earlier finding that adult but not juvenile RGS ignore information regarding response urgency encoded in the rate of juvenile produced repetitive calls, our present results suggest a developmental shift in response‐urgency perception. Adult RGS selectively extract information regarding response urgency via discrimination of the number of callers, ignoring less reliable information encoded in the rate of repetitive calls issued by inexperienced juvenile signallers.     

Headwaters are critical reservoirs of microbial diversity for fluvial networks

Streams and rivers form conspicuous networks on the Earth and are among nature''s most effective integrators. Their dendritic structure reaches into the terrestrial landscape and accumulates water and sediment en route from abundant headwater streams to a single river mouth. The prevailing view over the last decades has been that biological diversity also accumulates downstream. Here, we show that this pattern does not hold for fluvial biofilms, which are the dominant mode of microbial life in streams and rivers and which fulfil critical ecosystem functions therein. Using 454 pyrosequencing on benthic biofilms from 114 streams, we found that microbial diversity decreased from headwaters downstream and especially at confluences. We suggest that the local environment and biotic interactions may modify the influence of metacommunity connectivity on local biofilm biodiversity throughout the network. In addition, there was a high degree of variability in species composition among headwater streams that could not be explained by geographical distance between catchments. This suggests that the dendritic nature of fluvial networks constrains the distributional patterns of microbial diversity similar to that of animals. Our observations highlight the contributions that headwaters make in the maintenance of microbial biodiversity in fluvial networks.