Comparative Predation on Naturally Occurring Gypsy Moth (Lepidoptera: Lymantriidae) Pupae and Deployed Freeze-Dried Pupae

Predation is an important factor in the dynamics of gypsy moth (Lymantria dispar L.) populations, yet predation rates can be difficult to estimate accurately in the field. Biased estimates can result from spatial heterogeneity in risk or from artifacts associated with deploying prey. Here we compare predation rates on freeze-dried gypsy moth pupae affixed with beeswax to pieces of burlap with predation rates on naturally occurring live pupae in the same sites. Daily predation rates, primarily by small mammals, were two to eight times greater for freeze-dried deployed pupae than natural pupae, depending on the year. These results indicate apparent predation rates can be substantially biased by artifacts associated with deployed prey, such as human scent, artificial substrates, or freeze drying. Results from studies using similar methods may provide qualitative comparisons of relative predation risk, but their estimates of absolute predation rates should be interpreted with caution, and attempts should be made to quantify and correct for any resulting bias

Spatial selection and inheritance: applying evolutionary concepts to population dynamics in heterogeneous space.

Organisms in highly suitable sites generally produce more offspring, and offspring can inherit this suitability by not dispersing far. This combination of spatial selection and spatial inheritance acts to bias the distribution of organisms toward suitable sites and thereby increase mean fitness (i.e., per capita population increase). Thus, population growth rates in heterogeneous space change over time by a process conceptually analogous to evolution by natural selection, opening avenues for theoretical cross-pollination between evolutionary biology and ecology. We operationally define spatial inheritance and spatial selective differential and then combine these two factors in a modification of the breeder\u27s equation, derived from simple models of population growth in heterogeneous space. The modified breeder\u27s equation yields a conservative criterion for persistence in hostile environments estimable from field measurements. We apply this framework for understanding gypsy moth population persistence amidst abundant predators and find that the predictions of the modified breeder\u27s equation match initial changes in population growth rate in independent simulation output. The analogy between spatial dynamics and natural selection conceptually links ecology and evolution, provides a spatially implicit framework for modeling spatial population dynamics, and represents an important null model for studying habitat selection

Limited Dispersal and Heterogeneous Predation Risk Synergistically Enhance Persistence of Rare Prey

White-footed mice prey on gypsy moth pupae while foraging for other, more abundant food. Mice appear capable of locally extirpating moths since mice exert high predation pressure on sparse pupae and are numerically decoupled from moth populations. Nevertheless, during 23 years of monitoring, moths persisted at scales .1 ha despite frequent extinctions at smaller spatial scales. We hypothesized that spatially heterogeneous intensity in mouse foraging and/or limited moth dispersal might allow moth persistence. Using a spatially explicit, individual-based, empirically parameterized model, we show that neither spatially heterogeneous predation by mice, nor limited moth dispersal alone allows moth persistence at typical mouse densities. However, synergy between both factors allows moth population persistence at naturally occurring mouse densities. For example, in models with 40 mice/ha, both limited moth dispersal with spatially homogeneous predation risk and spatially heterogeneous predation risk with unlimited moth dispersal had a 0% chance of moth persistence, but the combination of limited dispersal and heterogeneous predation risk resulted in a ~75% chance of moth persistence. Furthermore, both for limited moth dispersal with spatially homogeneous predation risk and for spatially heterogeneous predation risk with unlimited moth dispersal, moth persistence was only guaranteed at very low mouse densities, while the combination of limited moth dispersal with heterogeneous predation guaranteed moth persistence within a broad range of mouse densities. The findings illustrate a novel mechanism of ‘‘spatial selection and satiation’’ that can enhance rare species persistence under intense incidental predation by generalist predators

Effect of feeding frequency on survival and growth of juvenile spiny lobster Panulirus versicolor in Indonesia

This research aimed to assess the effect of feeding frequency on survival and growth of juvenile bamboo spiny lobster Panulirus versicolor (Latreille, 1804). A completely randomized design of 4 treatments with 4 replicates was used with treatments consisting of: feeding once per day (FR1), feeding twice per day (FR2); feeding three times per day (FR3) and feeding four times per day (FR4). The experiment was performed in a tank system with a recirculating water supply. Sixteen 100 litre tanks were stocked with post-puerulus juveniles, mean weight 0.50±0.01 g, at a density of 89 m-2 and the experiment ran for 30 days. Diet consisted of a manufactured pellet diet formulated for tropical spiny lobster. Results indicated a statistically significant effect (p < 0.05) of feeding frequency on carapace length, although not for other variables. Carapace length for feeding two and four times per day was significantly greater than for feeding once per day. Mean survival rate across all treatments was 32% and mean final weight was 0.95 g. Notwithstanding the statistical non-significance for several of the variables, the significant effect on carapace length and trends evident for the other variables suggest feeding more than once per day may be beneficial

Boom‐bust dynamics in biological invasions: towards an improved application of the concept

Boom‐bust dynamics – the rise of a population to outbreak levels, followed by a dramatic decline – have been associated with biological invasions and offered as a reason not to manage troublesome invaders. However, boom‐bust dynamics rarely have been critically defined, analyzed, or interpreted. Here, we define boom‐bust dynamics and provide specific suggestions for improving the application of the boom‐bust concept. Boom‐bust dynamics can arise from many causes, some closely associated with invasions, but others occurring across a wide range of ecological settings, especially when environmental conditions are changing rapidly. As a result, it is difficult to infer cause or predict future trajectories merely by observing the dynamic. We use tests with simulated data to show that a common metric for detecting and describing boom‐bust dynamics, decline from an observed peak to a subsequent trough, tends to severely overestimate the frequency and severity of busts, and should be used cautiously if at all. We review and test other metrics that are better suited to describe boom‐bust dynamics. Understanding the frequency and importance of boom‐bust dynamics requires empirical studies of large, representative, long‐term data sets that use clear definitions of boom‐bust, appropriate analytical methods, and careful interpretations

Quantifying a Dynamic Risk Landscape: Heterogeneous Predator Activity and Implications for Prey Persistence

Spatial heterogeneity in predation risk can ameliorate impacts on prey populations, particularly for prey of generalists. Spatially heterogeneous risk implies the existence of refugia, and the spatial scale of those refugia and their persistence over time affect whether prey can avoid predation by aggregating therein. Our objective was to quantify the magnitude, spatial scale, and temporal persistence of heterogeneity in risk of predation by white-footed mice (Peromyscus leucopus), an abundant generalist predator of gypsy moths (Lymantria dispar) and songbirds. We used track plates to measure white-footed mouse activity at .170 trees in each of three forest plots in upstate New York during summers of 2003–2005. We quantified the mean and coefficient of variation of track activity among trees by fitting the beta-binomial distribution to data from each plot and study period. We measured temporal persistence by disattenuated autocorrelation, and spatial scale by fitting exponential variograms. Mice were much less abundant in 2005 than the other two years, leading to lower overall track activity but higher coefficient of variation among trees. Mouse track activity at individual trees was positively autocorrelated between monthly study periods in 2003 and 2004, and even between the two years, whereas temporal autocorrelation in 2005 was much weaker. Track activity showed positive spatial autocorrelation over lag distances from ;30 to .1000 m. These findings indicate that mouse activity, and hence risk to their prey, varies substantially in space at spatial and temporal scales that appear responsive to mouse population dynamics. The spatial scale and temporal persistence of that variation imply that prey may benefit from returning to, or failing to disperse from, refugia

Use of Track Plates to Quantify Predation Risk at Small Spatial Scales

Spatial heterogeneity in risk is a critical component of predator-prey interactions. However, at small spatial scales, it is difficult to quantify predation risk without altering it. We used track plates to measure local predation risk created by white-footed mouse (Peromyscus leucopus) foraging activity on oak-forest plots in Millbrook, New York. Live gypsy moth pupae (Lymantria dispar) were placed at 2 heights on trees and monitored for predation. Pupae deployed on trees visited by mice were more likely to be eaten than those on trees not visited. Logistic regression indicated that predation rates on gypsy moth pupae were positively correlated with track activity, indicating that areas of concentrated mouse activity were areas of heightened risk for gypsy moths. Survival of individual oat grains placed on and 50 cm from track plates were not statistically different, indicating that mice exhibited no detectable behavioral reaction toward track plates. We conclude that track plates offer an economical and reliable means of quantifying local risk of attack by terrestrial mammals without substantially altering the spatial distribution of risk

Summer 1982

Registration of Isofenphos (page 3) Managing Annual Bluegrass (4) Helminthosporium Leaf Spot Fungicide Control Trial--1981 (8) Cultivar Trials--1981 (9) Dollar Spot (Sclerotinia Homeocarpa Sp.) Fungicide Control Trial--1981 (14) Living with the Gypsy Moth (15

Variation in Isoprene Emission from Quercus rubra: Sources, Causes, and Consequences for Estimating Fluxes

Isoprene is the dominant volatile organic compound produced in many forest systems. Uncertainty in estimates of leaf level isoprene emission rate stems from an insufficient understanding of the patterns and processes controlling isoprene emission capacity in plant leaves. Previous studies suggest that variation in isoprene emission capacity is substantial; however, it is not known at what scale emission capacity is the most variable. Identifying the sources of variation in emission capacity has implications for conducting measurements and for model development, which will ultimately improve emission estimates and models of tropospheric chemistry. In addition, understanding the sources of variation will help to develop a comprehensive understanding of the physiological controls over isoprene emission. This study applied a variance partitioning approach to identify the major sources of variation in isoprene emission capacity from two populations of northern red oak (Quercus rubra) over three growing seasons. Specifically, we evaluated variation due to climate, populations, trees, branches, leaves, seasons, and years. Overall, the dominant source of variation was the effect of a moderate drought event. In the years without drought events, variation among individual trees (intraspecific) explained approximately 60% of the total variance. Within the midseason, isoprene emission capacity of sun leaves varied by a factor of 2 among trees. During the third year a moderate 20-day drought event caused isoprene emission capacity to decrease fourfold, and the relative importance of intraspecific variation was reduced to 24% of total variance. Overall, ambient temperature, light, and a drought index were poor predictors of isoprene emission capacity over a 0 to 14-day period across growing seasons. The drought event captured in this study emphasizes the need to incorporate environmental influences into leaf level emission models

An Intron 7 Polymorphism in APP Affects the Age of Onset of Dementia in Down Syndrome

People with Down syndrome (DS) develop Alzheimer's disease (AD) with an early age of onset. A tetranucleotide repeat, attt5−8, in intron 7 of the amyloid precursor protein has been associated with the age of onset of AD in DS in a preliminary study. The authors examine the impact of this polymorphism in a larger cohort of individuals with DS. Adults with DS were genotyped for attt5−8 and APOE. The results were analysed with respect to the age of onset of dementia. The presence of three copies of the six-repeat allele resulted in onset of dementia seven years earlier than in the presence of other genotypes. Further study is essential to elucidate the mechanism by which this polymorphism functions, with an exciting opportunity to identify novel treatment targets relevant for people with DS and AD