摘要
An individual-based population dynamics model (IBM) was used to examine the effect of different behavioral, bioenergetic, and physiological assumptions on individual growth and development of the copepod, Metridia lucens, in the North Atlantic Ocean. Both intrinsic (nutritional condition, feeding history, size) and extrinsic (temperature, food resources) factors that might determine individual growth and development rates were examined. An advantage of an IBM is that it allows for inter-individual variability, and can thereby provide an indication of the range of responses that might arise from natural variation in environmental conditions. The model is a refinement of an earlier model that successfully reproduced the observed stage structure and abundance of Metridia pacifica in the sub-arctic Pacific (Batchelder and Miller, 1989). Consequently, parameters for the ingestion and metabolic functions were set initially to those found appropriate for M. pacica from previous model studies. Extrinsic forcing variables used to drive the population model were depth-specific temperature and chlorophyll a concentration. The model was run in two modes: chronological and individual. In the former mode, the model used measured temperature and chlorophyll a data to reproduce the life-history timing (phenology) and seasonal stage-structure of a M. lucens population measured in the early 1970s from Ocean Weather Station India in the North Atlantic. The individual mode was used to examine variation in growth caused by inter-individual variability in short-medium term starvation and feeding success. Ingestion, growth, and development were sensitive to variations in food resources. Factors that increased consumption rates, such as more effective searching for high chlorophyll layers, or recent starvation resulting in a “hunger response” in the functional response relation, led to markedly faster growth and development rates. Model simulations indicate that inter-individual variability in growth dynamics decreased for copepods capable of plasticity in the physiological hunger response or more effective food-searching behavior. Such searching behavior accentuated already existing inter-annual and intra-annual differences in individual growth dynamics forced by temperature and food. Conversely, hunger acclimation reduced intra-annual (seasonal) variability and reduced, although only slightly, inter-annual variability in growth dynamics. These model results highlight the importance of understanding how copepods respond to environmental conditions. Two methods — behavioral modification and physiological acclimation - by which copepods might ameliorate low food conditions, lead to different responses to temporal and spatial variability of resources.