Carry over from previous year environmental conditions alters dominance hierarchy in a prairie plant community

Aims To determine if an experimentally applied anomalous weather year could have effects on species composition and community structure that would carry over into the following year.Methods We conducted a field experiment applying two levels of temperature(ambient and+4
C)and two levels of precipitation(ambient and doubled)and followed cover of plant species during the treatment year and one post-treatment year.Data analysis included ordination analysis,examination of species frequency distributions and comparison of cover of functional groups and individual species.Important Findings A drought during the summer and fall of the treatment year resulted in significant differences in community structure between the 2 years.C3 and winter annual species were depressed in the spring of the second year following the dry autumn.Species richness and legume cover increased in the second,wetter,year.Treatments caused no overall differences in community structure but did alter the dominance hierarchy of species among treatments as well as years.Warming decreased relative cover of winter annuals and early spring-flowering species but increased other annuals.Warming and double precipitation together increased cover of C4 perennial graminoids.In particular,the warming and precipitation treatments both increased the abundance of Andropogon gerardii,not individually altering the dominance hierarchy but together nearly doubling the relative cover of A.gerardii,making it the most abundant species in the combined treatment,while the cover of Bromus arvensis,the former dominant,decreased by 25%.The following year,Andropogon relative cover increased further in the former warmed plots,becoming dominant in both the formerly warmed and warmed plus double precipitation treatments.The year following treatments also saw an increase in relative cover of summer-blooming species in the formerly warmed plots and differences among the former treatments in species richness of functional groups.If the effects of one anomalous year on plant abundance can carry over into the following year,several warm years could have a significant impact on plant community structure.

Aviary measurements of dominance and affiliation between members of mixed-species birds flocks in southern China

In mutualistic interactions,all parties are usually considered to benefit;yet there may be asymmetries in mutualisms where some partners/individuals benefit more than others.Such is thought to be the case in mixedspecies flocks of birds,where following species are thought to benefit more than leading species,and leading species may not be able to escape the association if they are subordinate to other species.We measured dominance and affiliation patterns of a mixed-species flock system of southern China in an aviary where these variables could be measured in a standardized way.In eight wild-caught flocks,the leading species,David’s Fulvetta(Alcippe davidi),was usually among the more subordinate flock members(ranking 9 of 13 species,with the the most dominant species ranked number one,and dominance measured by normalized David’s scores).Dominance was strongly influenced by body mass,and not by bill length or the number of individuals.Female fulvettas in particular tended to be among the most subordinate individuals in the flock.There was evidence of a negative relationship between a species pair’s affiliation,measured as the percentage of all observations in which these two species were found perching together,and their difference in ranking in the dominance hierarchy,particularly when some ground species,which are not likely to remain in flocks long term,were removed from the analysis.Species pairs that had more pronounced differences in their dominance rankings were less likely to be affiliated,which is consistent with the idea that subordinate species may avoid dominants.David’s Fulvetta is a strong information provider,so other species are likely benefitted in this relationship.Our data suggest one reason that fulvettas stay in flocks is that they may be subordinate and therefore have little control over who associates with them.

Factors influencing the establishment of dominance hierarchies of the grey triggerfish Balistes capriscus

Unlike other balistids, grey triggerfish Balistes capriscus occur in social groups in subtropical reef assemblages and have been noted to cooperate in capturing large crustacean prey. The objective of this study were to determine the structure of dominance hierarchies of these social groups and the factors that influence hierarchies of wild-caught grey triggerfish in a natu- ralistic setting. From observations of four groups of triggerfish （n = 19 fish） in both dyad and group （4 - 5 fish） settings, we provide a description of triggerfish behaviors and coloration patterns and an explanation of the social context in which suites of behaviors are used by dominant, middle-ranking, and subordinate fish. Sixteen behaviors and nine coloration patterns were noted for grey triggerfish. Grey triggerfish groups form linear hierarchies in both dyads and groups as measured by Landau＇s lndex of Linearity （h = 1.0 for Groups 1, 3, and 4 and h = 0.95 for Group 2 in dyads; h = 1.0 for all groups in group settings）. Dyadic hierarchies, however, were not necessarily good predictors of the hierarchies found in larger group settings, as they only predicted two of the four group hierarchies. Sex played no role in influencing status or behavior. Size had the greatest influence on domi- nance status, with larger fish being more dominant than smaller fish. An individual＇s dominance ranking influenced both body coloration and posture. These results suggest that color patterns and body postures may also be used by observers as an indicator of an individual＇s social status in groups [Current Zoology 56 （1）： 18-35, 2010].