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PubMed2002

Generation of periodic waves by landscape features in cyclic predator-prey systems.

The vast majority of models for spatial dynamics of natural populations assume a homogeneous physical environment. However, in practice, dispersing organisms may encounter landscape features that significantly inhibit their movement. We use mathematical modelling to investigate the effect of such landscape features on cyclic predator-prey populations. We show that when appropriate boundary conditions are applied at the edge of the obstacle, a pattern of periodic travelling waves develops, moving out and away from the obstacle. Depending on the assumptions of the model, these waves can take the form of roughly circular 'target patterns' or spirals. This is, to our knowledge, a new mechanism for periodic-wave generation in ecological systems and our results suggest that it may apply quite generally not only to cyclic predator-prey interactions, but also to populations that oscillate for other reasons. In particular, we suggest that it may provide an explanation for the observed pattern of travelling waves in the densities of field voles (Microtus agrestis) in Kielder Forest (Scotland-England border) and of red grouse (Lagopus lagopus scoticus) on Kerloch Moor (northeast Scotland), which in both cases move orthogonally to any large-scale obstacles to movement. Moreover, given that such obstacles to movement are the rule rather than the exception in real-world environments, our results suggest that complex spatio-temporal patterns such as periodic travelling waves are likely to be much more common in the natural world than has previously been assumed.

Animals↗
PubMed2002

Habitat destruction in a simple predator-prey patch model: how predators enhance prey persistence and abundance.

We model a metapopulation of predator-prey patches using both spatially implicit or mean-field (MF) and spatially explicit (SE) approaches. We show that in the MF model there are parameter regimes for which prey cannot persist in the absence of predators, but can in their presence. In addition, there are parameter regimes for which prey may persist in isolation, but the presence of predators will increase prey patch density. Predators may thus enhance prey persistence and overall abundance. The key mechanism responsible for this effect is the occurrence of prey dispersal from patches that are occupied by both prey and predators. In addition, these patches should be either long-lived, such as that occurs when predators keep prey from overexploiting its local resource, or the presence of a predator on a patch should significantly enhance the prey dispersal out of that patch. In the SE approach these positive effects of predators on prey persistence and abundance occur for even larger parameter ranges than in the MF model. Prey dispersal from predator-prey patches may thus be important for persistence of both species as a community, independent of the modeling framework studied. Comparison of the MF and SE approaches shows that local dispersal constraints can have the edge over global dispersal for the persistence of the metapopulation in regimes where the two species have a beneficial effect on each other. In general, our model provides an example of feedback in multiple-species metapopulations that can make the implementation of conservation schemes based on single-species arguments very risky.

Animals↗
PubMed2005

Patterns of male residency and intergroup transfer in gray-cheeked mangabeys (Lophocebus albigena).

We describe the movements and fates of 36 collared gray-cheeked male mangabeys (Lophocebus albigena) that resided in seven social groups in Kibale National Park, Uganda. The male mangabeys were captured, radiotagged, and then contacted regularly over a period of up to 8 years. Individuals varied considerably in how tightly they were associated with their groups. "Central" males were usually found in close spatial association with their own groups, but they sometimes visited others. "Peripheral" males were often found several hundred meters away from their own groups. Most adult males were characterized by repeated intergroup transfers, manifested as "visits" and "dispersals." Visits were transfers that did not result in mating. The visits were brief, and ranged from a few minutes to a few days before the male returned to his previous group, moved on to another group, or returned to solitary life. The term "dispersal" refers to a transfer that results in mating, after which the male remains in the new group. Young males began to drift away from their natal groups in early subadulthood, but the timing of first associations with estrous females in other groups was highly variable. Natal dispersers were generally solitary for a month or more, and at least half moved into nonadjacent groups. Secondary dispersal was common. After they immigrated, adult males remained in a group for a median of 19 months before they emigrated again, with the probability of departure being approximately constant in time. Secondary dispersal was usually made into an adjacent group and lasted less than 7 days. Emigration and immigration were not seasonal, and males emigrated singly and apparently independently; however, immigrations were clumped in time, and male dispersal contributed to considerable heterogeneity of group composition. L. albigena dispersal patterns are intermediate between those described for Papio baboons and forest Cercopithecus, and models that predict demographic consequences of dispersal for baboons can be refined to apply to mangabeys.

Animals↗
PubMed2005

Response to novel housing in two groups of captive tufted capuchin monkeys (Cebus apella).

The influence of age, maternal status, and the presence of a group male on use of space was assessed in two groups of captive tufted capuchin monkeys that underwent a move from indoor housing to a larger outdoor facility. Both groups originally contained two adult males, but only one group retained a male after the move. Following the move, mothers spent less time on the ground when carrying their infants than they did when not carrying their infants. In the group with no male (1) individuals decreased time spent on the ground relative to pre-move levels, whereas no such difference was noted in the group with the male; (2) females spent more time carrying their infants than did females in the group with a male. In the group with the adult male, juveniles spent less time on the ground than did non-mother adult females, whereas no difference had existed prior to the move. Grooming rates dropped from pre-move to post-move, but the mean number of partners with which each animal was in contact increased. Measures of social behavior varied across post-move observation periods inversely to time spent on the ground. These results are consistent with the view that an individual's relative vulnerability influences behavioral conservatism in novel environments, and suggests a relatively profound role for males in promoting exploration of new space in this species.

Age Factors↗
PubMed2006

Quantitative analysis of temporal and spatial variations of chondrocyte behavior in engineered cartilage during long-term culture.

In this work, we present the fact that chondrocyte activity differs in relation to their position in an engineered cartilage construct. Chondrocytes from porcine articular cartilage were cultured in a monolayer. Then the cell/extracellular matrix (ECM) membrane was peeled off and centrifuged into a three-dimensional (3D) pellet-type construct. Cultivated in a static condition, the constructs were harvested at specific time intervals (1, 2, 3, and 5 weeks) and manually cored using a biopsy punch to separate the core from the remaining construct. The resultant parts, core and peripheral remnant were thus obtained and subjected to analysis individually. Cell density (10(6 )cells/cm(3)) of the core was significantly higher at 1 week than that of the periphery but this trend was reversed at later time points. Cell viability was remarkably better in the peripheral tissue. Alcian blue staining of glycosaminoglycan (GAG) revealed an intense blue staining from the periphery, exhibiting a steep gradient in distribution of GAG concentration. The gene expression ratio of collagen type II to I appeared to be more altered in the periphery, possibly suggesting cell dedifferentiation, especially at later time points (>2 weeks). The mRNA levels of matrix metalloproteinase-1 (MMP-1) and MMP-13 remained in the normal range, whereas collagen type X expression was more significantly upregulated at the periphery. This study showed that chondrocyte behavior could be highly variable in the extent of their proliferation, differentiation and dedifferentiation, depending on their physical location within 3D engineered cartilage construct.

Animals↗
PubMedDate not supplied

Effects of delay, intertrial interval, delay behavior and trimethyltin on spatial delayed response in rats.

Working memory was modeled in rats using a delayed response task with spatial location as the discriminative cue. Rats received food for pressing 1 of 2 retractable levers in the choice phase of a trial if that lever had been presented in the prior sample phase of that trial. When delays of 0-20 sec were imposed between sample and choice, choice accuracy declined with increasing delay. With short intertrial intervals (ITIs), choice accuracy decreased more at long delays than at short delays, showing that interference from previous trials impaired memory but not discrimination. Rats emitted overt mediating responses during delay by pressing the levers in the retracted position. However, the frequency of delay presses was low (less than 2/trial in all rats) and neither their frequency nor accuracy was related to choice accuracy. Resetting the delay interval for each delay press did not significantly alter choice response accuracy. Trimethyltin (TMT), 7 mg/kg IV, reduced the choice accuracy of one rat to chance levels at all delays; two other rats were affected transiently. TMT reduced choice accuracy during weeks 1 and 4 postinjection, with significant effects on the linear slope and intercept of the mean retention gradient during week 4. TMT did not affect responses to the retracted levers during delays. TMT treatment also elevated levels of glial fibrillary acidic protein (GFAP) in the CNS, measured 4 weeks after treatment. Hippocampal GFAP correlated highly with the reduction in choice accuracy during week 1 (r = -.903) and week 4 (r = -.797) postTMT.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed2004

Animals' use of landmarks and metric information to reorient: effects of the size of the experimental space.

Disoriented children could use geometric information in combination with landmark information to reorient themselves in large but not in small experimental spaces. We tested fish in the same task and found that they were able to conjoin geometric and non-geometric (landmark) information to reorient themselves in both the large and the small space used. Moreover, fish proved able to reorient immediately when dislocated from a large to a small experimental space and vice versa, suggesting that they encoded the relative rather than the absolute metrics of the environment. However, fish tended to make relatively more errors based on geometric information when transfer occurred from a small to a large space, and to make relatively more errors based on landmark information when transfer occurred from a large to a small space. The hypothesis is discussed that organisms are prepared to use only distant featural information as landmarks.

Animals↗
PubMed2005

Ant navigation: reading geometrical signposts.

Ants often travel along complex pheromone trail systems between their nest and foraging areas. A new and surprising discovery is that Pharaoh's ants can work out from the geometry of individual branch points on the trail whether they are heading towards or away from the nest.

Animals↗
PubMed2006

Ant navigation: one-way routes rather than maps.

In recent years, there has been an upsurge of interest and debate about whether social insects-central-place foragers such as bees and ants-acquire and use cognitive maps, which enable the animal to steer novel courses between familiar sites . Especially in honey bees, it has been claimed that these insects indeed possess such "general landscape memories" and use them in a "map-like" way . Here, we address this question in Australian desert ants, Melophorus bagoti, which forage within cluttered environments full of nearby and more distant landmarks. Within these environments, the ants establish landmark-based idiosyncratic routes from the nest to their feeding sites and select different one-way routes for their outbound and inbound journeys. Various types of displacement experiments show that inbound ants when hitting their inbound routes at any particular place immediately channel in and follow these routes until they reach the nest, but that they behave as though lost when hitting their habitual outbound routes. Hence, familiar landmarks are not decoupled from the context within which they have been acquired and are not knitted together in a more general and potentially map-like way. They instruct the ants when to do what rather than provide them with map-like information about their position in space.

Animals↗
PubMed2005

Three-month-olds' sensitivity to orientation cues in the three-dimensional depth plane.

Three-month-olds are sensitive to orientation changes of line drawings when they have a three-dimensional (3-D) interpretation and when the changes are defined by both 3-D depth and two-dimensional (2-D) picture plane cues [Bhatt, R. S., & Bertin, E. (2001). Pictorial cues and three-dimensional information processing in early infancy. Journal of Experimental Child Psychology, 80, 315-332]. In the current study, we examined whether 3-month-olds are sensitive to pictorial line junction cues that signal orientation changes solely in the 3-D depth plane. The results revealed that infants discriminated a misoriented elongated cube in an array when the stimuli contained both shading and lines (Experiment 2) but not when only lines depicted the elongated cubes (Experiment 1). Testing with comparable 2-D images revealed that, even in the presence of shading information, detection of orientation changes is specific to images that have a 3-D interpretation. Together, the results suggest that 3-month-olds are sensitive to pictorial line junction cues that signal orientation changes in the 3-D depth plane to adults provided that shading information is available and the images have a 3-D interpretation.

Cues↗
PubMed2005

Egocentric path integration models and their application to desert arthropods.

Path integration enables desert arthropods to find back to their nest on the shortest track from any position. To perform path integration successfully, speeds and turning angles along the preceding outbound path have to be measured continuously and combined to determine an internal global vector leading back home at any time. A number of experiments have given an idea how arthropods might use allothetic or idiothetic signals to perceive their orientation and moving speed. We systematically review the four possible model descriptions of mathematically precise path integration, whereby we favour and elaborate the hitherto not used variant of egocentric cartesian coordinates. Its simple and intuitive structure is demonstrated in comparison to the other models. Measuring two speeds, the forward moving speed and the angular turning rate, and implementing them into a linear system of differential equations provides the necessary information during outbound route, reorientation process and return path. In addition, we propose several possible types of systematic errors that can cause deviations from the correct homeward course. Deviations have been observed for several species of desert arthropods in different experiments, but their origin is still under debate. Using our egocentric path integration model we propose simple error indices depending on path geometry that will allow future experiments to rule out or corroborate certain error types.

Animals↗
PubMed1995

Psychophysical assessment of toddlers' ability to cope with slopes.

This research examined how infants in early stages of walking determine whether a hill is safe or risky for locomotion. A psychophysical staircase procedure provided estimates of infants' physical ability to walk up and down slopes (2 degrees to 36 degrees), and a "go ration" indexed the accuracy of their perceptual judgments. On average, perceptual judgments were scaled to walking ability on slopes. Children walked on safe slopes and balked on risky ones. For ascent, perceptual judgments were related to length of walking experience and walking skill on flat ground. Better walkers were also better perceivers. For descent, judgments neatly mirrored exploratory activity. Better perceivers explored hills more efficiently by hesitating, touching, and testing different positions on hills around the limits of their physical ability.

Exploratory Behavior↗
PubMed2005

How independent are parallel memory systems? A theoretical comment on Gibson and Shettleworth (2005).

Using only behavioral manipulations, B. M. Gibson and S. J. Shettleworth (2005) have shown that rats can simultaneously acquire both place and response information. Experiments in which these 2 kinds of information are presented sequentially (response followed by place), provide some evidence for blocking of place learning, suggesting an influence of information acquired by a response-learning system on the subsequent acquisition of information by a place-learning system. A detailed examination of the results in the context of information about the kinds of learning that take place on a maze suggests that the memory processes underlying the rats' behavior in this experiment were considerably more complex than is acknowledged by Gibson and Shettleworth. The discussion illustrates the importance of considering both behavioral and physiological information for understanding how learning and memory functions are organized in the brain.

Animals↗
PubMed2006

Spared feature-structure discrimination but diminished salience of environmental geometry in hippocampal-lesioned homing pigeons (Columba livia).

Homing pigeons (Columba livia) were trained to locate a goal in one corner of a rectangular arena by either its shape (geometry) or the left-right configuration of colored features located in each corner (feature structure). Control and hippocampal-lesioned pigeons learned at a similar rate, but the control birds made proportionally more geometric errors during acquisition. On conflict probe trials, the control birds preferred geometrically correct corners, whereas the hippocampal-lesioned birds displayed a greater preference for the correct corner defined by feature structure. On geometry-only probe trials, both groups demonstrated an ability to identify the goal location. Hippocampal lesions do not interfere with goal recognition by the feature structure of local cues but diminish the salience of arena shape.

Animals↗