Aging and demographic plasticity in response to experimental age structures in honeybees (<Emphasis Type="Italic">Apis mellifera</Emphasis> L)

Honeybee colonies are highly integrated functional units characterized by a pronounced division of labor. Division of labor among workers is mainly age-based, with younger individuals focusing on in-hive tasks and older workers performing the more hazardous foraging activities. Thus, experimental disruption of the age composition of the worker hive population is expected to have profound consequences for colony function. Adaptive demography theory predicts that the natural hive age composition represents a colony-level adaptation and thus results in optimal hive performance. Alternatively, the hive age composition may be an epiphenomenon, resulting from individual life history optimization. We addressed these predictions by comparing individual worker longevity and brood production in hives that were composed of a single-age cohort, two distinct age cohorts, and hives that had a continuous, natural age distribution. Four experimental replicates showed that colonies with a natural age composition did not consistently have a higher life expectancy and/or brood production than the single-cohort or double-cohort hives. Instead, a complex interplay of age structure, environmental conditions, colony size, brood production, and individual mortality emerged. A general tradeoff between worker life expectancy and colony productivity was apparent, and the transition from in-hive tasks to foraging was the most significant predictor of worker lifespan irrespective of the colony age structure. We conclude that the natural age structure of honeybee hives is not a colony-level adaptation. Furthermore, our results show that honeybees exhibit pronounced demographic plasticity in addition to behavioral plasticity to react to demographic disturbances of their societies.     

Impact of marine protected areas on temporal stability of fish species diversity

Preserving biodiversity over time is a pressing challenge for conservation science. A key goal of marine protected areas (MPAs) is to maintain stability in species composition, via reduced turnover, to support ecosystem function. Yet, this stability is rarely measured directly under different levels of protection. Rather, evaluations of MPA efficacy generally consist of static measures of abundance, species richness, and biomass, and rare measures of turnover are limited to short-term studies involving pairwise (beta diversity) comparisons. Zeta diversity is a recently developed metric of turnover that allows for measurement of compositional similarity across multiple assemblages and thus provides more comprehensive estimates of turnover. We evaluated the effectiveness of MPAs at preserving fish zeta diversity across a network of marine reserves over 10 years in Batemans Marine Park, Australia. Snorkel transect surveys were conducted across multiple replicated and spatially interspersed sites to record fish species occurrence through time. Protection provided by MPAs conferred greater stability in fish species turnover. Marine protected areas had significantly shallower decline in zeta diversity compared with partially protected and unprotected areas. The retention of harvested species was four to six times greater in MPAs compared with partially protected and unprotected areas, and the stabilizing effects of protection were observable within 4 years of park implementation. Conversely, partial protection offered little to no improvement in stability, compared with unprotected areas. These findings support the efficacy of MPAs for preserving temporal fish diversity stability. The implementation of MPAs helps stabilize fish diversity and may, therefore, support biodiversity resilience under ongoing environmental change.