The objective of this study was to use hierarchical phytosociological data to clarify the process of succession from a native willow riparian forest to one dominated by the invasive species Robinia pseudoacacia. We applied two-way indicator species analysis (TWINSPAN) and species-composition data obtained from vegetation surveys. In community-classification approaches, the species composition of each community type is often clarified using the highest value of cover rank for each species in each vertical forest layer. However, this method cannot elucidate distributional relationships among the upper and lower layers, so it cannot provide information on succession or species shifts among communities. In this study, we analyzed species distributions in terms of individual cover in each of the tall-tree, sub-tree, shrub, and herb layers using the TWINSPAN method, which distinguishes the distributional structures of the upper and lower layers. The TWINSPAN results for our hierarchical data show that Robinia pseudoacacia persisted beneath tall-growth willow (Salix serissaefolia), which was dominant in the riparian zone, but that S. serissaefolia seedlings and shrubs did not grow in the understory of the R. pseudoacacia forest canopy. These results imply that in the absence of large-scale disturbance by river water native S. serissaefolia forests will shift toward non-native R. pseudoacacia forests. Our results indicate that TWINSPAN is useful for understanding forest regeneration and succession involving invasive species, in particular, even in the absence of tree-height and stem-diameter data from surveys of individual trees.
Biomechanics is the study of the morphology and motion of the mechanical aspects of biological systems. Broadly, an organism’s behavior is the result of accumulated motion; its morphology and locomotion, which are under mechanical constraints, affect the organism’s fitness via energy balance. Explorations of the mechanisms of biological systems have uncovered universal principles and functions of motion. Despite its wide implications, this field has been considered highly niche. We suggest that this perception can be overcome by addressing a wide range of questions across research themes in ecology. For example, there is growing interest in evolutionary biomechanics (i.e., mechanistic analysis of trade-offs between the functions and constraints of a given trait) as an effective path to addressing persistent evolutionary questions. Furthermore, we believe that biomechanics will continue to develop as an ecological field in its own right and in association with other fields. Here, we discuss current contributions of biomechanics to the field of ecology using representative research examples.
Endothermy is the regulation of body temperature using metabolic heat, while ectothermy is the regulation of body temperature using external heat sources. Reptiles are generally ectothermic animals, but some large marine reptiles are known to be highly endothermic and to maintain their body temperatures at above environmental temperatures. An animal’s body temperature is determined by the balance of thermal energy entering and leaving the body and is closely related to body size and metabolic rate. In this paper, I focus on sea turtles as endothermic marine reptiles and explain how they maintain body temperatures elevated above water temperatures, focusing on body size and metabolic heat. In addition, I also show differences in observed resting metabolic rates and body temperatures between two genetically isolated populations of loggerhead turtles and discuss the ecological implications of this difference.
Body temperature has a profound influence on animal activity through its thermodynamic effects on metabolism. The body temperature of ectotherms depends on the external temperature environment and, in contrast to the autonomous thermoregulation of endotherms, ectotherms adjust their body temperature using behavioral responses. Although behavioral thermoregulation is useful against daily temperature variations, it is not capable of coping with seasonal or annual temperature fluctuations. Under temperature fluctuations, ectotherms adjust their thermal sensitivities through plastic and/or genetic physiological changes. In the present review, salmonids are introduced as examples of the thermal adaptations of ectotherms. Most salmonids show strong fidelity to their natal streams for spawning, and this fidelity has resulted in genetically and geographically distinct populations within species. Salmonids are generally recognized as stenothermic and cold-adapted fishes but the temperature environments experienced by different populations are diverse. Indeed, it has been shown that in some salmonid species each population becomes locally adapted through the alteration of metabolic traits. I will review the thermal adaptation of fishes based on studies that clarify the links between the thermal performance of metabolic traits and environmental temperature in salmonids.
The thermal environment of the ocean changes drastically with depth, and fish can actively regulate their body temperatures through short-term vertical migrations. The larger a fish’s body size, the greater its thermal inertia, and the longer it can remain outside its preferred temperature range. In this paper, foraging strategies used by fish to catch prey in environments outside their preferred temperature range are discussed in terms of thermoregulation, using the example of the ocean sunfish Mola mola, which makes deep dives to feed on deep-sea jellyfish. With variations in dive duration, the proportion of time spent moving increased when the dive was short, and the proportion of time spent in body temperature recovery increased when the dive was long. Thus, there is a dive duration that maximizes foraging time. This dive duration was estimated to increase with prey depth and fish body size. This may be an example of the optimal foraging theory whereby foraging time is increased through the efficient use of thermal resources rather than food resources.
Animal movement requires energy. The cost of movement includes the locomotion required to move through space as well as the metabolic cost of maintaining homeostasis during movement. Thus, there is a trade-off between the costs of locomotion and metabolism, given that the latter increases proportionately with movement duration. In the case of ectothermic animals, the thermal environment affects an individual’s metabolic activity, and thus limits its use of space within a temperature range. Recent developments in the fields of bio-logging and biomechanics have allowed us to understand how movement costs are reduced in animals via morphology and movement pattern. For example, hydrodynamic body shapes and cost-efficient movement strategies greatly reduce locomotive costs in aquatic environments. The trade-off in costs over the duration of a given movement can be used to predict theoretically the optimal movement strategy of an animal; in many cases, these predictions are validated by behavioural observations in the field. This approach may be effective for understanding the morphological and behavioural diversity of many animal taxa and predicting their fate in changing environments.