... Training in preference which occurs as a result of larger number of encounters (termed &q... more ... Training in preference which occurs as a result of larger number of encounters (termed "training bias" by Bryan 1973, who reviews the literature) has been found in starfish by Landenberger (1968); in snails by Murdoch ... Search image formation in the blue jay (Cyanocitta cristata ...
Sediment pollution is a major cause of stream degradation throughout the United States. Quantifyi... more Sediment pollution is a major cause of stream degradation throughout the United States. Quantifying this pollution and understanding erosion risk is important for decision makers, but also problematic. Data at the catchment scale is often limited by availability, cost, representativeness, and reliability, making it unrealistic to assess erosion risk over a large area. While many models estimate overland flow related soil loss, streambank erosion is often overlooked and can be the dominant source of sediment in a catchment. We used the Enhanced Generalized Watershed Loading Functions (GWLF-E) model and MapShed plugin for MapWindow GIS to simulate the water budget, field erosion from the landscape, and streambank erosion in 20 subbasins along a gradient of agricultural to urban land cover from 1997-2015 in the Indian Mill Creek watershed of Michigan, USA. Annual water budget results suggest the creek is primarily groundwater fed, but that a per-subbasin average of 6% to 15% of precipitation becomes runoff. Field erosion contributed a per-subbasin average of 0.5 to 2.5 Mg ha-1 yr-1 of sediment, while streambank erosion accounted for 0.2% to 50.1% of the subbasins' total sediment yields. Average lateral erosion rate of streambanks in subbasins ranged from 0.04 to 7.37 cm yr-1, with 4 subbasins exceeding 1.0 cm yr-1. Urban areas had more streambank erosion than agricultural segments due the runoff from impervious surfaces. Our findings suggest that models that simulate both field and streambank erosion can provide valuable data to prioritize restoration programs that reduce sediment loading.
Abstract The scope of current optimal diet theory is greatly restricted by certain rather stringe... more Abstract The scope of current optimal diet theory is greatly restricted by certain rather stringent assumptions upon which it rests. One of these is that the type of prey a predator encounters next is not influenced by the last type encountered. The purpose of this paper ...
Explaining spatiotemporal variability in metacommunities is challenging because conducting empiri... more Explaining spatiotemporal variability in metacommunities is challenging because conducting empirical studies that link mechanisms across scales is difficult. We developed a stochastic model of epilithic algal succession in streams to better understand the underlying interactions that drive patch dynamics at three levels of spatial hierarchy: patch, channel habitat, and reach. The state of an algal patch is specified by one of nine community types, which are defined by growth form. Ninety‐two empirical data sets of epilithic succession were used to estimate Markov transition probabilities among patch types as functions of inputs for light, nutrients, and current. Two additional probability matrices determine the effects of herbivory and disturbance based on user inputs. Testing model predictions of patch composition against independent empirical data indicated good correspondence based on resemblance metrics. Early in succession, most patches were occupied by prostrate and erect diatoms. These persisted under low light and nutrient conditions. Motile and stalked diatom patches characterized later stages when resources were moderate. Succession proceeded to mostly filamentous green algal patches under high resource levels. Sensitivity simulations indicated light most affected succession. Herbivory and disturbance increased the probability of prostrate diatom patches. We then used the model to examine how changes in abiotic and biotic parameters affect patch dynamics at different scales. Changes in nutrients or light affected patch diversity differently at the habitat vs. reach scale. Interactions with local resource levels within a channel habitat determined its alpha diversity. The proportion of channel habitat types within a reach, and their collective response to changes, determined beta diversity. Patch diversity within channel habitats generated by herbivory followed the predation hypothesis only when nutrients were low. At the reach scale, herbivory always increased patch similarity among channel habitats, lowering beta diversity. Diversity within channel habitats followed the intermediate disturbance hypothesis for a variety of habitats. Effects of disturbance on beta diversity at the reach scale depended on channel habitat heterogeneity. The stability of patches at the reach scale was highest when disturbance created high patch diversity, supporting the insurance hypothesis. The ideas generated can improve stream bioassessment methods and provide insight into mechanisms underlying patch dynamics in other ecosystems.
Prior theoretical studies have shown that the juvenile period's length is an important de... more Prior theoretical studies have shown that the juvenile period's length is an important determinant of local stability in age-structured population dynamics. For example, both short and long periods produce stability, but intermediate lengths can cause instability. Short juvenile periods significantly increase stability (compared to no juvenile period) if fecundity is independent of adult age. Here I re-examine these and other patterns, using a model which includes a variable juvenile period, juvenile mortality, density-dependent fecundity and adult mortality, and age-dependence is adult fecundity. Among other things, the results confirm the stable-unstable-stable pattern with increasing juvenile period length, but show that the stabilizing effect of short periods disappears when fecundity varies with adult age. Broadly speaking, the results suggest that age-dependence in adult fecundity has important dynamical consequences, and that models assuming that fecundity is independent of adult age may be unreliable guides to the dynamics of populations for which this assumption is not reasonably accurate.
Host-parasite interactions may lead to a variety of outcomes. Trematode infection of pulmonate sn... more Host-parasite interactions may lead to a variety of outcomes. Trematode infection of pulmonate snails is often associated with increased growth and/or survivorship of snail hosts. We use the freshwater pulmonate Lymnaea elodes and its trematode parasites to ...
Krebs et al.(1974) predicted that an optimal forager in a patchy habitat should apply the same gi... more Krebs et al.(1974) predicted that an optimal forager in a patchy habitat should apply the same giving-up time (GUT) to all patches, even if they differ in quality. This prediction has repeatedly appeared in the literature. However, it is based on a model which is not ...
Abstract Sexual reproduction is known to be an important means of propagation for native Japanese... more Abstract Sexual reproduction is known to be an important means of propagation for native Japanese knotweed populations in Asia. For naturalized populations in the United States, however, its relative importance compared with propagation by rhizome and stem ...
In laboratory studies, rotifers (Brachionus calyciflorus) were monitored under well-defined envir... more In laboratory studies, rotifers (Brachionus calyciflorus) were monitored under well-defined environmental conditions at different supply rates of a unicellular algal food (Chlorella vulgaris). Rotifer size frequency distributions are described for conditions of steady-state growth, exponential increase, and starvation. Temporal fluctuations in size-age structure are described for cultures during transient conditions during the approach to a steady state and following step changes in food supply rate. The size structures of the populations displayed definite and reproducible shifts among typical patterns during transient conditions, reflecting the physiological and other dynamic processes that underlay the population dynamics. Size structure probably is a key variable that should be included in models for predicting growth dynamics during transient growth conditions.
... Training in preference which occurs as a result of larger number of encounters (termed &q... more ... Training in preference which occurs as a result of larger number of encounters (termed "training bias" by Bryan 1973, who reviews the literature) has been found in starfish by Landenberger (1968); in snails by Murdoch ... Search image formation in the blue jay (Cyanocitta cristata ...
Sediment pollution is a major cause of stream degradation throughout the United States. Quantifyi... more Sediment pollution is a major cause of stream degradation throughout the United States. Quantifying this pollution and understanding erosion risk is important for decision makers, but also problematic. Data at the catchment scale is often limited by availability, cost, representativeness, and reliability, making it unrealistic to assess erosion risk over a large area. While many models estimate overland flow related soil loss, streambank erosion is often overlooked and can be the dominant source of sediment in a catchment. We used the Enhanced Generalized Watershed Loading Functions (GWLF-E) model and MapShed plugin for MapWindow GIS to simulate the water budget, field erosion from the landscape, and streambank erosion in 20 subbasins along a gradient of agricultural to urban land cover from 1997-2015 in the Indian Mill Creek watershed of Michigan, USA. Annual water budget results suggest the creek is primarily groundwater fed, but that a per-subbasin average of 6% to 15% of precipitation becomes runoff. Field erosion contributed a per-subbasin average of 0.5 to 2.5 Mg ha-1 yr-1 of sediment, while streambank erosion accounted for 0.2% to 50.1% of the subbasins' total sediment yields. Average lateral erosion rate of streambanks in subbasins ranged from 0.04 to 7.37 cm yr-1, with 4 subbasins exceeding 1.0 cm yr-1. Urban areas had more streambank erosion than agricultural segments due the runoff from impervious surfaces. Our findings suggest that models that simulate both field and streambank erosion can provide valuable data to prioritize restoration programs that reduce sediment loading.
Abstract The scope of current optimal diet theory is greatly restricted by certain rather stringe... more Abstract The scope of current optimal diet theory is greatly restricted by certain rather stringent assumptions upon which it rests. One of these is that the type of prey a predator encounters next is not influenced by the last type encountered. The purpose of this paper ...
Explaining spatiotemporal variability in metacommunities is challenging because conducting empiri... more Explaining spatiotemporal variability in metacommunities is challenging because conducting empirical studies that link mechanisms across scales is difficult. We developed a stochastic model of epilithic algal succession in streams to better understand the underlying interactions that drive patch dynamics at three levels of spatial hierarchy: patch, channel habitat, and reach. The state of an algal patch is specified by one of nine community types, which are defined by growth form. Ninety‐two empirical data sets of epilithic succession were used to estimate Markov transition probabilities among patch types as functions of inputs for light, nutrients, and current. Two additional probability matrices determine the effects of herbivory and disturbance based on user inputs. Testing model predictions of patch composition against independent empirical data indicated good correspondence based on resemblance metrics. Early in succession, most patches were occupied by prostrate and erect diatoms. These persisted under low light and nutrient conditions. Motile and stalked diatom patches characterized later stages when resources were moderate. Succession proceeded to mostly filamentous green algal patches under high resource levels. Sensitivity simulations indicated light most affected succession. Herbivory and disturbance increased the probability of prostrate diatom patches. We then used the model to examine how changes in abiotic and biotic parameters affect patch dynamics at different scales. Changes in nutrients or light affected patch diversity differently at the habitat vs. reach scale. Interactions with local resource levels within a channel habitat determined its alpha diversity. The proportion of channel habitat types within a reach, and their collective response to changes, determined beta diversity. Patch diversity within channel habitats generated by herbivory followed the predation hypothesis only when nutrients were low. At the reach scale, herbivory always increased patch similarity among channel habitats, lowering beta diversity. Diversity within channel habitats followed the intermediate disturbance hypothesis for a variety of habitats. Effects of disturbance on beta diversity at the reach scale depended on channel habitat heterogeneity. The stability of patches at the reach scale was highest when disturbance created high patch diversity, supporting the insurance hypothesis. The ideas generated can improve stream bioassessment methods and provide insight into mechanisms underlying patch dynamics in other ecosystems.
Prior theoretical studies have shown that the juvenile period's length is an important de... more Prior theoretical studies have shown that the juvenile period's length is an important determinant of local stability in age-structured population dynamics. For example, both short and long periods produce stability, but intermediate lengths can cause instability. Short juvenile periods significantly increase stability (compared to no juvenile period) if fecundity is independent of adult age. Here I re-examine these and other patterns, using a model which includes a variable juvenile period, juvenile mortality, density-dependent fecundity and adult mortality, and age-dependence is adult fecundity. Among other things, the results confirm the stable-unstable-stable pattern with increasing juvenile period length, but show that the stabilizing effect of short periods disappears when fecundity varies with adult age. Broadly speaking, the results suggest that age-dependence in adult fecundity has important dynamical consequences, and that models assuming that fecundity is independent of adult age may be unreliable guides to the dynamics of populations for which this assumption is not reasonably accurate.
Host-parasite interactions may lead to a variety of outcomes. Trematode infection of pulmonate sn... more Host-parasite interactions may lead to a variety of outcomes. Trematode infection of pulmonate snails is often associated with increased growth and/or survivorship of snail hosts. We use the freshwater pulmonate Lymnaea elodes and its trematode parasites to ...
Krebs et al.(1974) predicted that an optimal forager in a patchy habitat should apply the same gi... more Krebs et al.(1974) predicted that an optimal forager in a patchy habitat should apply the same giving-up time (GUT) to all patches, even if they differ in quality. This prediction has repeatedly appeared in the literature. However, it is based on a model which is not ...
Abstract Sexual reproduction is known to be an important means of propagation for native Japanese... more Abstract Sexual reproduction is known to be an important means of propagation for native Japanese knotweed populations in Asia. For naturalized populations in the United States, however, its relative importance compared with propagation by rhizome and stem ...
In laboratory studies, rotifers (Brachionus calyciflorus) were monitored under well-defined envir... more In laboratory studies, rotifers (Brachionus calyciflorus) were monitored under well-defined environmental conditions at different supply rates of a unicellular algal food (Chlorella vulgaris). Rotifer size frequency distributions are described for conditions of steady-state growth, exponential increase, and starvation. Temporal fluctuations in size-age structure are described for cultures during transient conditions during the approach to a steady state and following step changes in food supply rate. The size structures of the populations displayed definite and reproducible shifts among typical patterns during transient conditions, reflecting the physiological and other dynamic processes that underlay the population dynamics. Size structure probably is a key variable that should be included in models for predicting growth dynamics during transient growth conditions.
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Papers by James McNair