No abstract

There is increasing evidence that size variability within a cohort can have important consequences on community ecology and evolution. It is commonly assumed that the threat of predation can influence cohort size variability by homogenizing foraging behavior among members. We combined predictions of growth-defense models with those from models of genesis of size variation to test the non-lethal effects of size-selective newt and gapeunconstrained aeshnid dragonfly larva predators on the size structure of Rhacophorus arboreus tadpoles in a controlled laboratory experiment. We hypothesized that the predators would induce differential growth and behavioral responses in the tadpoles, and would decrease cohort size variation. The tadpoles reduced activity levels in the presence of the predators, but the responses were generally stronger in the presence of dragonfly larvae. Growth costs were commensurate with the levels of behavioral defense investments in the tadpoles. Despite strong reductions in activity levels and growth, cohort size variation increased in the presence of predators, contrasting current models on relationship between foraging rates, growth, and cohort size variation in prey. The underlying mechanisms are unclear, but it is possible that reduced rates of movement limited access to food for some cohort members or that predation risk enhanced the expression of behavioral variation among individuals.

Highlights• The canopy gaps induced by wind/snowstorm were aggregated in steep slope and high altitude areas, while the gaps formed by flood were gathered in steep slope and low altitude areas.• The wind/snowstorm mainly driven the formation of medium gaps, while the flood mainly promoted the percentage of small gaps and vacant lands. AbstractCanopy gap is the driving force of forest succession. Due to the uncontrollability, however, the influences of natural disturbances on gap formation and gap distribution pattern have been rarely understood in temperate secondary forest ecosystems. We monitored the gap formation and gap distribution pattern using high-resolution remote sensing images before and after two disturbances (wind/snowstorm in 2003 and flood in 2013). The results showed that after wind/snowstorm, the gap nearest neighbor index (GNNI) decreased, the vacant land area did not obviously change while the gap fraction and gaps density (especially medium size) increased. After the flood, GNNI decreased, the number of small gaps increased but larger gaps were in many cases extended to vacant land areas leading to a smaller total number of medium and large gaps but considerable increase in vacant land area. We also found that the gap densities increased with slope and altitude for wind/snowstorm-formed gaps, but they increased with increasing slope and decreasing altitude for flood-formed gaps. These results indicated that gaps were aggregated in steep slope and high altitude areas after wind/snowstorm, but in steep slope and low altitude areas after the flood. Medium gaps were mainly created by the wind/snowstorm due to the individual-level death of dominant tree with the continuous fall of surrounding trees. While, vacant lands were obviously created during the flood because of integral sweeping. Besides, smaller trees were easily damaged by runoff of flood, which induced small gaps. In summary, forest managers may pay more attention to use gaps to accelerate forest succession after wind/snowstorms and to restore vegetation in vacant lands after floods.