Amphibious animals may be subject to strong but conflicting selective pressures to enhance locomotor performance both on land and in the water. Biomechanical models suggest that in snakes, adaptations to swimming (e.g. reduction of ventral plates, flattening of tail) will reduce their ability to move on land. The locomotor speeds of six taxa of amphibious (laticaudid) sea‐snakes, plus one entirely marine (hydrophiid) species were measured. Because the relative dependence on aquatic vs terrestrial habitats varies with a laticaudid's species, sex and body size, a previous study predicted that these factors should generate significant variation in locomotor speeds within laticaudids. Measurements of swimming and crawling speeds supported this prediction. Some species were faster than others and, within each species, males were faster than conspecific females. The degree of locomotor superiority of males was greater for terrestrial (>40%) than for aquatic (20%) locomotion. Smaller snakes were faster than larger animals in relative speed (body lengths/s) but slower in absolute terms (m/s). The hydrophiid Emydocephalus annulatus was slow in water as well as on land, perhaps because it eats immobile prey and thus, does not depend on speed for foraging. The diversity of locomotor abilities within laticaudid sea‐snakes provides a remarkable opportunity to identify factors that influence evolutionary trade‐offs between conflicting evolutionary optima.

Despite wide recognition of their significant role in explaining sustained growth and economic development, uncompensated knowledge spillovers have not yet been fully modeled with a microeconomic foundation. The main purpose of this paper is to illustrate the exchange of knowledge as well as its consequences on agglomerative activity in a general-equilibrium search-theoretic framework. Agents, possessing differentiated types of knowledge, search for partners to exchange ideas and create new knowledge in order to improve production efficacy. When individuals' types of knowledge are too diverse, a match is less likely to generate significant innovations. We demonstrate the extent of agglomeration has significant implications for the patterns of information flows in economies. Further, by simultaneously determining the patterns of knowledge exchange and the spatial agglomeration of an economy we identify additional channels for interaction between agglomerative activity and knowledge exchange. Finally, contrary to previous work in spatial agglomeration, our model suggests that agglomerative environments may be either under-specialized and under-populated or over-specialized and over-populated relative to the social optimum.

Despite wide recognition of their significant role in explaining sustained growth and economic development, uncompensated knowledge spillovers have not yet been fully modeled with a microeconomic foundation. The main purpose of this paper is to illustrate the exchange of knowledge as well as its consequences on agglomerative activity in a general-equilibrium search-theoretic framework. Agents, possessing differentiated types of knowledge, search for partners to exchange ideas and create new knowledge in order to improve production efficacy. When individuals' types of knowledge are too diverse, a match is less likely to generate significant innovations. We demonstrate the extent of agglomeration has significant implications for the patterns of information flows in economies. Further, by simultaneously determining the patterns of knowledge exchange and the spatial agglomeration of an economy we identify additional channels for interaction between agglomerative activity and knowledge exchange. Finally, contrary to previous work in spatial agglomeration, our model suggests that agglomerative environments may be either under-specialized and under-populated or over-specialized and over-populated relative to the social optimum.

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We study the use of money for sharing consumption risk. In our model, agents randomly receive endowments at some points in time and produce at other points. Due to information frictions, agents cannot use intertemporal contracts to share risk. The use of money allows agents to overcome these information frictions. The Friedman rule is shown to generate efficient risk sharing. Furthermore, we quantify the welfare costs of incomplete risk sharing and find that with 10% inflation, the welfare cost of inefficient risk sharing is approximately 1%-1.5% of steady-state consumption.