23 research outputs found

    Checkerboard Patterns, Interspecific Competition, and Extinction: Lessons from Distribution Patterns of Tarsiers (Tarsius) and Slow Lorises (Nycticebus) in Insular Southeast Asia

    Get PDF
    Tarsiers (Tarsius) and slow lorises (Nycticebus) are the only extant nocturnal primates occurring in Southeast Asia. Harcourt (1999) hypothesized that in insular Southeast Asia, slow lorises and tarsiers showed a checkerboard distribution on 12 small (<12,000 km2) islands, i.e., only one or the other occurs, and attributed this to extreme levels of competition between these 2 largely faunivorous primates. Further, he predicted slow lorises were able to persist on smaller islands than tarsiers. We re-evaluated these findings using an expanded dataset including 49 islands where tarsiers or slow lorises occur. Tarsiers and slow lorises live on islands of similar size (median size of ca. 300–900 km2), and both taxa inhabit an equal proportion of small, medium, and large islands. On small islands within their area of sympatry tarsiers occur on 1 island, slow lorises on 8, both genera on 3, and we can assume they have become extinct from 11 small islands since the Last Glacial Maximum. Sizes of islands where tarsiers or slow lorises have become extinct do not differ from islands where they are still extant. We show that slow lorises occur on more islands in insular Southeast Asia than perhaps previously assumed, but these islands are not smaller on average than islands where tarsiers occur. A checkerboard distribution between these taxa is not evident. More studies are needed at the macroecological level to assess the importance of biogeographic history in explaining their present-day distribution patterns

    The evolution of the upright posture and gait—a review and a new synthesis

    Get PDF
    During the last century, approximately 30 hypotheses have been constructed to explain the evolution of the human upright posture and locomotion. The most important and recent ones are discussed here. Meanwhile, it has been established that all main hypotheses published until the last decade of the past century are outdated, at least with respect to some of their main ideas: Firstly, they were focused on only one cause for the evolution of bipedality, whereas the evolutionary process was much more complex. Secondly, they were all placed into a savannah scenario. During the 1990s, the fossil record allowed the reconstruction of emerging bipedalism more precisely in a forested habitat (e.g., as reported by Clarke and Tobias (Science 269:521–524, 1995) and WoldeGabriel et al. (Nature 412:175–178, 2001)). Moreover, the fossil remains revealed increasing evidence that this part of human evolution took place in a more humid environment than previously assumed. The Amphibian Generalist Theory, presented first in the year 2000, suggests that bipedalism began in a wooded habitat. The forests were not far from a shore, where our early ancestor, along with its arboreal habits, walked and waded in shallow water finding rich food with little investment. In contrast to all other theories, wading behaviour not only triggers an upright posture, but also forces the individual to maintain this position and to walk bipedally. So far, this is the only scenario suitable to overcome the considerable anatomical and functional threshold from quadrupedalism to bipedalism. This is consistent with paleoanthropological findings and with functional anatomy as well as with energetic calculations, and not least, with evolutionary psychology. The new synthesis presented here is able to harmonise many of the hitherto competing theories

    A sensory-driven controller for quadruped locomotion

    No full text
    Locomotion of quadruped robots has not yet achieved the harmony, flexibility, efficiency and robustness of its biological counterparts. Biological research showed that spinal reflexes are crucial for a successful locomotion in the most varied terrains. In this context, the development of bio-inspired controllers seems to be a good way to move toward an efficient and robust robotic locomotion, by mimicking their biological counterparts. This contribution presents a sensory-driven controller designed for the simulated Oncilla quadruped robot. In the proposed reflex controller, movement is generated through the robot's interactions with the environment, and therefore, the controller is solely dependent on sensory information. The results show that the reflex controller is capable of producing stable quadruped locomotion with a regular stepping pattern. Furthermore, it is capable of dealing with slopes without changing the parameters and with small obstacles, overcoming them successfully. Finally, system robustness was verified by adding noise to sensors and actuators and also delays.This work has been supported by FCT-Fundacao para a Ciência e Tecnologia in the scope of the project: PEst-UID/CEC/00319/2013.info:eu-repo/semantics/publishedVersio
    corecore