Identification of tree groups used by secondary cavity-nesting birds to simplify forest management in subtropical forests

In tropical and subtropical forest ecosystems,cavities formed by decay processes are a key but scarce resource for birds that nest and roost in them,which makes them a highly sensitive group to logging.The piedmont forest of northwestern Argentina is a complex ecosystem with 113 tree and 120 bird species.It has high logging pressure on the few,well-conserved forest remnants,complicating the delineation of sustainable management guidelines for each tree or bird species in a short time.Our objective was to reduce the complexity of subtropical forests by grouping tree species according to the characteristics used by secondary cavity-nesting birds(i.e.non excavators).In the piedmont forest,50 plots of 0.25 ha were sampled to record cavity trees and cavity characteristics.These were then used in a cluster analysis to form tree groups.Additionally,cavities were searched to identify the bird species using the decay-formed cavities.A total of 187 cavity trees,comprising 23 tree species,were recorded,and these formed four tree groups or clusters.We recorded 86 cavities that were used by secondary cavitynesting bird species.The four tree groups were unequally used by secondary cavity nesters.The tree group that included valuable timber species(Myroxylon peruiferum,Anadenanthera colubrina and Calycophyllum multiflorum)and had the greatest cavity availability represented 71%of total cavity use.Another tree group with valuable timber species(Cedrela balansae and Amburana cearensis),measured>73 cm DBH and>21 m tall,had cavity entrances>0.10 cm2,and contributed 14%of all cavity use by birds.A third group had no highly economically valuable tree species,and included the snag category(i.e.standing dead trees)as well as a 15%of cavity use.The fourth tree group had a DBH<0.40 cm,only one highly economically valuable tree species(Cordia trichotoma),and supported no cavity use.The clustering of subtropical trees can reduce the complexity of these forests,hence easing their management by focusing on those groups with tree species showing similar characteristics and providing suitable nesting sites for secondary cavity-nesting birds.

Relatedness dynamics and sex-biased dispersal in a seasonal cycle of corn mice from intensively managed agroecosystems

The sex-biased dispersal and kinship dynamics are important factors shaping the spatial distribution of individuals and are key parameters affecting a variety of ecological and evolutionary processes.Here,we studied the spatial distribution of related individuals within a population of corn mice Calomys musculinus in a seasonal cycle to infer dispersal patterns.The sampling was carried out from spring 2005 to winter 2006 in field borders of intensively managed agroecosystems.Genotyping data from 346 individuals with 9 microsatellites showed spatial genetic structure was weak for males,but not for females.The results indicate a complex spatial kinship dynamic of related females across all seasons.Which,contrary to our expectations,dispersal distances decrease with the increase of the population abundance.Meanwhile,male dispersal distances were greater when population abundance increased and thus the availability of active females.Males disperse greater distances to mate and sire offspring with distant females as a possible inbreeding avoidance mechanism.This study shows that C.musculinus is capable of much greater scattering distances than previously reported and that dispersal occurs fluidly and without barriers across the agroecosystem.The indirect benefit of dispersal on individual fitness could be related to relaxing the competition in the natal area and increasing the mating rate.Our study highlights the value of combining genetic relatedness,fieldwork observations,and behavioral data to estimate dispersal at a fine geographical scale.

Setting large-and medium-sized mammal restoration goals in a last mountain Chaco remnant from central Argentina

Background Setting large-and medium-sized wild mammal(≥2 kg)restoration goals is important due to their role as ecosystem engineers and generalized numeric reductions.However,determining wild mammal restoration goals is very challenging due to difficulties in obtaining data on current mammal density and due to unclear information on what mammal density values should be used as a reference.Here we chose a 154 ha conservation area within one of the last remnants of the mountainous Chaco from central Argentina.We suspected that extensive and unreported defaunation had occurred due to past human pressure and the introduction of non-native mammals.To conduct the analyses,we used a simplified technique that integrates methods used in rangeland and ecological sciences.Results Eight native mammal species including only one herbivore species,and four non-native mammal species including three herbivore species were detected during 6113 camera trap days.We used known cattle densities as estimated by droppings and direct counts,together with the relative abundance indexes obtained from camera trap photos to calculate the densities of the other species,correcting for mammal size.Densities for the least and most abundant native species were 0.2 and 1.33 individuals km^(-2),respectively;and for non-native species,0.03 and 5.00 individuals km^(-2),respectively.Native and non-native species represented 0.8%and 99.2%,respectively,of the bio-mass estimates.Reference values for native herbivore biomass,as estimated from net primary productivity,were 68 times higher than values estimated for the study area(3179 vs.46.5 kg km^(-2)).Conclusions There is an urgent need to increase native mammals,with special emphasis on herbivore biomass and richness,while non-native mammal numbers must be reduced.As cattle are widespread in large portions of the globe and there is a lot of experience estimating their abundances,the ratio method we used extrapolating from cattle to other large-and medium-sized mammals could facilitate estimating mammal restoration goals in other small and defaunated areas,where traditional methods are not feasible when target mammal densities get very low.