The effects of host plant species on adult oviposition and larval performance of the aphid predator Aphidoletes aphidimyza

1. Although preference–performance relationships in insects are typically studied in a bi-trophic context, it is well known that host plants can affect both the preference and performance of natural enemies of herbivorous insects. 2. This study presents evidence from field and laboratory studies that two species of milkweeds, the putatively less defended Asclepias incarnata and the putatively more defended Asclepias syriaca, differentially affect adult oviposition and larval performance in Aphidoletes aphidimyza, an aphid-feeding predatory midge, independent of aphid density. 3. Host plant species affected predatory fly larvae abundance by a factor of 50 in the field and a factor of 8 in the laboratory. Larval and adult emergence rates in our laboratory studies provided strong evidence for reduced performance on A. syriaca. Oviposition in choice and no-choice settings provided some evidence for preference for A. incarnata, and a potentially suppressive effect of A. syriaca. 4. The results provide limited support for the hypothesis that natural selection can lead to positive correlations between adult oviposition preferences and larval performance upon various food sources, even when predatory insects oviposit onto host plants of their herbivorous prey. 5. Preference and performance are not perfectly aligned in this system, however, because ovipositing females do not reject A. syriaca entirely. Potential explanations for mismatches between preference and performance in this system include the neural constraints associated with being a generalist, adaptive time-limited foraging strategies, and unique evolutionary histories of laboratory colonies compared with wild insects.     

Exotic grass invasion impacts fitness of an endangered prairie butterfly, <Emphasis Type="Italic">Icaricia icarioides fenderi</Emphasis>

Fender’s blue butterfly is an endangered species restricted to fragmented, grassland remnants that are becoming increasingly dominated by tall, invasive grasses in western Oregon, USA. I performed a removal experiment to assess the impacts of structural degradation accompanying the invasion of Arrhenatherum elatius, tall oat grass, on butterfly fitness and fitness related behaviors. Clipping of A. elatius to native grass sward height resulted in 2.5–5 times as many eggs laid per leaf of host plant. Both male and female butterflies basked more frequently in areas removed of A. elatius inflorescences and upon encountering the treatment edge butterflies had a high rate of return into a large area removed of the grass inflorescences. Although butterfly behavior appeared to be affected by the change in sward height on the treatment edge, there was no evidence for the edge causing a disproportionate egg load. Invasion and dominance by A. elatius appeared to diminish host plant apparency which may result in overloading of eggs on conspicuous host plants, increased incidence of emigration, and a decrease in the likelihood of colonization because female butterflies appeared indifferent to larval resources beneath A. elatius inflorescences. Dominance of natural shortgrass prairies by tall stature grasses like A. elatius may be an insidious form of habitat degradation for grassland Lepidoptera worldwide, but it may go largely unnoticed because larval and adult resources can persist under the unnaturally tall grass canopy.     

Central Place Foraging in Nonpatchy Habitats

This paper deal with a model of optimal foraging in a habitat with arbitrary food distribution. It takes into account an arbitrary risk cost related to the distance to the animal's nest. Food acquisition and risk cost are accounted for in common units of fitness. The resulting problem is solved in the context of Calculus of Variations. The optimal duration of absence from the nest and the optimal spatial allocation of foraging time are obtained: the optimal strategy leads to separate the habitat into a region to exploit and a region to ignore. The definition of these two distinct regions depends on the relative importance of risk and food availability. With realistic risk costs, the resulting strategy indicates a highly selective behaviour when far from the nest, as observed in field studies. The model is also extended to take account of the need of returning to the nest to guard it or to feed the young.     

An improved approach to evaluate car sharing options

We develop an improved approach to evaluate car sharing options under uncertain environments with the combination of Fuzzy Analytic Hierarchy Process (F-AHP) and Fuzzy Technique for Order Preference by Similarity to Ideal Solution (F-TOPSIS), which consists of three steps. In the first step, we propose a SCUMN (Specific, Comprehensive, Understandable, Measurable, and Neutral) methodology to identify appropriate indicators and obtain a final list of 24 indicators according to their relevance to car sharing options. In the second step, we determine the weight of each indicator with F-AHP and conduct consistency check of the comparison matrix of selected indicators. In the third step, comparison of different options is performed with selected indicators and F-TOPSIS. A case study is provided to validate the proposed approach. Twenty-four indicators are identified to evaluate five different car sharing options and rank them according to their closeness coefficients in decreasing order. And thirty-one sensitivity analysis experiments are conducted to figure out the influence of indicators on decision making. The experimental results show that the proposed approach is capable of evaluating car sharing options with uncertainty and vagueness. F-AHP is able to determine the weight for each selected indicator and F-TOPSIS demonstrates its advantage in comparing potential options.     

Can landscape properties predict occurrence of grey-sided voles?

There has been a long-term decline in spring and fall numbers of Clethrionomys rufocanus in boreal Sweden in 1971–2005. Previous studies on permanent sampling plots in the centre of 2.5 × 2.5 km landscapes suggested that habitat fragmentation (sensu destruction) could have contributed to the decline. Therefore, we tested these findings in a field study and compared trapping results on the central sampling plots of landscapes with a low degree of fragmentation (LDF) and of “hot spot” type with trapping results in managed forest landscapes with a high degree of fragmentation (HDF). We predicted that C. rufocanus would be more common on the LDF plots. We used our permanent plots supplemented with a new sample of plots, mainly of the rare LDF type, inside or just outside the long-term study area. Very few voles were trapped on both plot types, and no difference was found. However, a subsequent pilot study with trapping in a national park with large areas of pristine, unfragmented forest yielded more voles than in the managed, more fragmented, areas. Consequently, the initial field study data and some other recent data were also re-analysed from a “local patch quality” perspective. This alternative approach revealed the positive importance of large focal patches of forest >60 years old and their content of old-growth (pine) forest (>100 years). Interestingly, at the landscape level, the frequency distribution of patches of forest >60 years old, old-growth (>100 years), and especially of old-growth pine forest (>100 years), relative to the properties of plots with C. rufocanus, suggested that there are few forest patches left that are suitable for C. rufocanus. Our current results suggest that habitat fragmentation cannot be excluded as a contributing cause to the long-term decline of C. rufocanus in boreal Sweden.     

Does re-creation of extensive pasture-forest mosaics provide an economically sustainable way of nature conservation in Sweden''s forest dominated regions?

There is a major risk that many of the remaining semi-natural pastures in Swedish forest dominated regions will lose their grazing in the near future with lost biodiversity as a result. The reason is the high costs of grazing small pastures with cattle from generally small herds. The approaching decoupling of the present EU income support per head of cattle will increase the risk. Calculations based on economies of scale in beef production and opportunity cost of forest and arable land suggest that re-creating extensive pasture-forest mosaics consisting of existing semi-natural pastures and adjacent arable fields and forests can secure economically sustainable grazing. The risk of local extinction of grassland species due to habitat isolation is also lower in large mosaics than in small, scattered pastures.     

Vertical and horizontal distribution patterns of the giant sea anemone Heteractis crispa with symbiotic anemonefish on a fringing coral reef

The distribution patterns of the leathery sea anemone, Heteractis crispa, which contains an algal endosymbiont (zooxanthellae) and anemonefish, were investigated in relation to size distribution on a shallow fringing reef (3.2 ha, 0–4 m depth) in Okinawa, Japan. Individual growth and movements were also examined. Large individuals (>1,000 cm²) inhabited reef edges up to a depth of 4 m, while small anemone (<500 cm²) inhabited shallow reefs including inner reef flats. Individuals rarely moved, and their sizes were significantly correlated with their water depths. Growth of small anemones was negatively correlated with their distance from the reef edge, suggesting that reef edges provide more prey and lower levels of physiological stress. This study suggested that deep reef edges are suitable habitats for H. crispa. Large anemones were inhabited by large Amphiprion perideraion or large Amphiprion clarkii, both of which are effective defenders against anemone predators. Anemones that settle in deep reef edges may enjoy a higher survival rate and attain a large size because of their symbiotic relationship with anemonefish. However, early settlers do not harbor anemonefish. Their mortality rate would be higher in the deep edges than in shallow edges, the complicated topography of which provides refuge.     

Non‐parametric habitat models with automatic interactions

Questions: Can a statistical model be designed to represent more directly the nature of organismal response to multiple interacting factors? Can multiplicative kernel smoothers be used for this purpose? What advantages does this approach have over more traditional habitat modelling methods? Methods: Non‐parametric multiplicative regression (NPMR) was developed from the premises that: the response variable has a minimum of zero and a physiologically‐determined maximum, species respond simultaneously to multiple ecological factors, the response to any one factor is conditioned by the values of other factors, and that if any of the factors is intolerable then the response is zero. Key features of NPMR are interactive effects of predictors, no need to specify an overall model form in advance, and built‐in controls on overfitting. The effectiveness of the method is demonstrated with simulated and real data sets. Results: Empirical and theoretical relationships of species response to multiple interacting predictors can be represented effectively by multiplicative kernel smoothers. NPMR allows us to abandon simplistic assumptions about overall model form, while embracing the ecological truism that habitat factors interact.