The impact of patch encounter rate on patch residence time of female parasitoids increases with patch quality

Abstract.  1. For animal species that forage on patchily distributed resources, patch time allocation is of prime importance to their reproductive success. According to Charnov's marginal value theorem (MVT), the rate of patch encounter should influence negatively the patch residence time: as the rate of patch encounter decreases, the patch residence time increases. Moreover, the MVT predicts that animals should stay longer in high quality patches.
2. Using the aphid parasitoid Aphidius rhopalosiphi (Hymenoptera: Aphidiinae), the effects of these two factors (patch encounter rate and host density) were combined in order to test if the increment in patch residence time for a given decrease in patch encounter rate was larger for high quality patches than for low quality patches.
3. The results show a significant effect of the interaction between the two factors. In high host density patches, parasitoids spent more time if they experienced a low patch encounter rate, while in low host density patches, patch encounter rate had no significant effect on the patch residence time. This suggests that the response of A. rhopalosiphi females to patch encounter rate varied with host density in the patch. Moreover, the same interaction effect was observed for the number of ovipositor contacts on aphids.
4. Parasitoid females can use patch encounter rate to estimate patch density in the habitat but the effect of this estimate on their patch residence time is modulated by patch quality. Staying longer in a patch when patches are rare is more advantageous when the fitness gained by doing so is large. In low quality patches, the expected fitness gain is small and the female may gain more by leaving and taking her chance at finding another patch.     

On the role of patch density and patch variability in central-place foraging

Existing models of the foraging behavior of single-prey loaders in patchy environments differ on whether the optimal forager is predicted to stay in a patch until a prey is found, or to leave a patch for a next one if a prey is not found by a certain “deadline.” This article examines conditions on the probability distribution of prey density across patches that are necessary or sufficient for the existence of a finite, optimal deadline. It is shown that, for environments in which prey density is variable but never falls below some strictly positive level, a finite, optimal deadline exists when and only when the spatial density of patches is “high.” Also, a characterization is given of a large class of distributions (including the gamma distribution) for which a finite, optimal deadline exists for all levels of spatial density of patches.     

Stochastic patch exploitation model

A solitary animal is foraging in a patch consisting of discrete prey items. We develop a stochastic model for the accumulation of gain as a function of elapsed time in the patch. The model is based on the waiting times between subsequent encounters with the prey items. The novelty of the model is in that it renders possible–via parameterization of the waiting time distributions: the incorporation of different foraging situations and patch structures into the gain process. The flexibility of the model is demonstrated with different foraging scenarios. Dependence of gain expectation and variance of the parameters of the waiting times is studied under these conditions. The model allows us to comment upon some of the basic concepts in contemporary foraging theory.     

The ephemeral resource patch concept

Ephemeral resource patches (ERPs) – short lived resources including dung, carrion, temporary pools, rotting vegetation, decaying wood, and fungi – are found throughout every ecosystem. Their short-lived dynamics greatly enhance ecosystem heterogeneity and have shaped the evolutionary trajectories of a wide range of organisms – from bacteria to insects and amphibians. Despite this, there has been no attempt to distinguish ERPs clearly from other resource types, to identify their shared spatiotemporal characteristics, or to articulate their broad ecological and evolutionary influences on biotic communities. Here, we define ERPs as any distinct consumable resources which (i) are homogeneous (genetically, chemically, or structurally) relative to the surrounding matrix, (ii) host a discrete multitrophic community consisting of species that cannot replicate solely in any of the surrounding matrix, and (iii) cannot maintain a balance between depletion and renewal, which in turn, prevents multiple generations of consumers/users or reaching a community equilibrium. We outline the wide range of ERPs that fit these criteria, propose 12 spatiotemporal characteristics along which ERPs can vary, and synthesise a large body of literature that relates ERP dynamics to ecological and evolutionary theory. We draw this knowledge together and present a new unifying conceptual framework that incorporates how ERPs have shaped the adaptive trajectories of organisms, the structure of ecosystems, and how they can be integrated into biodiversity management and conservation. Future research should focus on how inter- and intra-resource variation occurs in nature – with a particular focus on resource × environment × genotype interactions. This will likely reveal novel adaptive strategies, aid the development of new eco-evolutionary theory, and greatly improve our understanding of the form and function of organisms and ecosystems.     

Transect-based patch size frequency analysis

Abstract. A new, transect-based patch size detection method for species pattern is proposed which improves results obtained with methods described earlier. The method was tested on an extensive artificial data set together with three of the existing methods considered best: Two and Three Term Local Quadrat Variance (T2LQV and T3LQV) and New Local Variance (NLV). The TLQV methods recovered only some of the existing patterns and were heavily dependent on inter-patch distances, whereas NLV almost always produced curves with oscillations. In addition a significance test is proposed, while such a test is seldom found in the earlier methods. Our method, PASFRAN, determines the frequencies of runs with 1, 2, 3, etc. quadrats containing a certain species and compares those with frequencies based on Monte Carlo simulated random configurations. The comparison is performed for each run length and the significance of the deviation between observed and expected frequencies can be calculated on the basis of a large number of simulations. Because this approach may be considered a case of multiple testing, a Bonferroni correction on the significance level was applied. The method can also be used for the detection of inter-patch distances. In addition, run lengths can be grouped and the test can be applied to the frequencies of combinations of run lengths. The method can detect dominance patches when quantitative data on the occurrence of plant species are available. In the same way, it can detect multi-species patterns using sample scores from an ordination analysis such as correspondence analysis. An extension towards composite, higher-order patterns is under investigation. The new method appeared to be effective in recovering artificial patterns, while it is not influenced by the relative values of patch size and inter-patch distance. When applied to the distribution of cow dung patches and certain plant species along a transect of 500 quadrats of 10 cm × 10 cm in an alvar limestone grassland, it produced straightforward and realistic results as compared with other methods and field impressions.     

The patch distributed producer-scrounger game

Grouping in animals is ubiquitous and thought to provide group members antipredatory advantages and foraging efficiency. However, parasitic foraging strategy often emerges in a group. The optimal parasitic policy has given rise to the producer-scrounger (PS) game model, in which producers search for food patches, and scroungers parasitize the discovered patches. The N-persons PS game model constructed by Vickery et al. (1991. Producers, scroungers, and group foraging. American Naturalist 137, 847-863) predicts the evolutionarily stable strategy (ESS) of frequency of producers that depends on the advantage of producers and the number of foragers in a group. However, the model assumes that the number of discovered patches in one time unit never exceeds one. In reality, multiple patches could be found in one time unit. In the present study, we relax this assumption and assumed that the number of discovered patches depends on the producers’ variable encounter rate with patches (λ). We show that strongly depends on λ within a feasible range, although it still depends on the advantage of producer and the number of foragers in a group. The basic idea of PS game is the same as the information sharing (parasitism), because scroungers are also thought to parasitize informations of locations of food patches. Horn (1968) indicated the role of information-parasitism in animal aggregation (Horn, H.S., 1968. The adaptive significance of colonial nesting in the Brewer's blackbird (euphagus cyanocephalus). Ecology 49, 682-646). Our modified PS game model shows the same prediction as the Horn's graphical animal aggregation model; the proportion of scroungers will increase or animals should adopt colonial foraging when resource is spatiotemporally clumped, but scroungers will decrease or animals should adopt territorial foraging if the resource is evenly distributed.     

Optimal patch residence time in egg parasitoids: innate versus learned estimate of patch quality

Charnovs marginal value theorem predicts that female parasitoids should exploit patches of their hosts until their instantaneous rate of fitness gain reaches a marginal value. The consequences of this are that: (1) better patches should be exploited for a longer time; (2) as travel time between patches increases, so does the patch residence time; and (3) all exploited patches should be reduced to the same level of profitability. Patch residence time was measured in an egg parasitoid Anaphes victus (Hymenoptera: Mymaridae) when patch quality and travel time, approximated here as an increased delay between emergence and patch exploitation, varied. As predicted, females stayed longer when patch quality and travel time increased. However, the marginal value of fitness gain when females left the patch increased with patch quality and decreased with travel time. A. victus females appear to base their patch quality estimate on the first patch encountered rather than on a fixed innate estimate, as was shown for another egg parasitoid Trichogramma brassicae. Such a strategy could be optimal when inter-generational variability in patch quality is high and within-generational variability is low.     

Inhibition of short patch and long patch base excision repair by an oxidized abasic site

5'-(2-Phosphoryl-1,4-dioxobutane) (DOB) is an oxidized abasic lesion that is produced by a variety of DNA damaging agents, including several antitumor antibiotics. DOB efficiently and irreversibly inhibits DNA polymerase β, an essential base excision repair enzyme in mammalian cells. The generality of this mode of inhibition by DOB is supported by the inactivation of DNA polymerase λ, which may serve as a possible backup for DNA polymerase β during abasic site repair. Protein digests suggest that Lys72 and Lys84, which are present in the lyase active site of DNA polymerase β, are modified by DOB. Monoaldehyde analogues of DOB substantiate the importance of the 1,4-dicarbonyl component of DOB for efficient inactivation of Pol β and the contribution of a freely diffusible electrophile liberated from the inhibitor by the enzyme. Inhibition of DNA polymerase β's lyase function is accompanied by inactivation of its DNA polymerase activity as well, which prevents long patch base excision repair of DOB. Overall, DOB is highly refractory to short patch and long patch base excision repair. Its recalcitrance to succumb to repair suggests that DOB is a significant source of the cytotoxicity of DNA damaging agents that produce it.     

Optimal patch use and metapopulation dynamics

Summary We compared the metapopulation dynamics of predator—prey systems with (1) adaptive global dispersal, (2) adaptive local dispersal, (3) fixed global dispersal and (4) fixed local dispersal by predators. Adaptive dispersal was modelled using the marginal value theorem, such that predators departed patches when the instantaneous rate of prey capture was less than the long-term rate of prey capture averaged over all patches, scaled to the movement time between patches. Adaptive dispersal tended to stabilize metapopulation dynamics in a similar manner to conventional fixed dispersal models, but the temporal dynamics of adaptive dispersal models were more unpredictable than the smooth oscillations of fixed dispersal models. Moreover, fixed and adaptive dispersal models responded differently to spatial variation in patch productivity and the degree of compartmentalization of the system. For both adaptive dispersal and fixed dispersal models, localized (stepping-stone) dispersal was more strongly stabilizing than global (island) dispersal. Variation among predators in the probability of dispersal in relation to local prey density had a strong stabilizing influence on both within-patch and metapopulation dynamics. These results suggest that adaptive space use strategies by predators could have important implications for the dynamics of spatially heterogeneous trophic systems.     

苦豆子斑块面积及斑块隔离度与豆荚螟发生情况的关联分析

破碎化生态格局中斑块面积和斑块隔离度对生物种群有一定的影响。苦豆子是宁夏荒漠半荒漠地区防风固沙的主要物种,其分布呈现典型的斑块化格局,豆荚螟是其种子的主要害虫。本文在宁夏灵武市宁东镇的余家湖(YJH,6个斑块)和羊场湾(YCW,7个斑块)两个样地共选择了13个苦豆子斑块,采用五点取样法采摘苦豆子豆荚,室内剥检统计害虫数量、豆荚及豆粒的危害率,用单因素方差分析进行差异性检验,用逐步回归法进行斑块面积、斑块隔离度与危害率的关联分析。结果显示:YJH样地斑块平均面积为2 629. 08 m~2,苦豆子平均盖度50. 33%,斑块间豆荚及豆粒危害率差异显著(P 0. 05); YCW样地斑块平均面积为1 010. 34 m~2,苦豆子平均盖度31. 14%,斑块间豆荚豆粒危害率差异不显著(P 0. 05)。13个斑块豆荚及豆粒的危害率均差异显著(P 0. 05)。斑块面积对豆荚螟数量的回归分析显示影响并不显著(R2=0. 084)。两样地间豆粒的危害率并无显著差异(P 0. 05); Pearson相关分析显示斑块连接度指数与豆荚危害率(r=-0. 2215)、豆粒危害率(r=-0. 4102)、豆荚螟数量(r=0. 0561)有一定的相关性。斑块面积对苦豆子种实害虫数量、豆荚及豆粒的危害率影响不显著,但斑块隔离度增加,能够减轻苦豆子种子害虫的危害。     

The effects of plant traits on species' responses to present and historical patch configurations and patch age

Patch configuration is viewed as an important factor affecting the distributions of plant species. Although a number of studies have explored the relationship between plant life‐history traits and species’ distributions in fragmented landscapes, the effect of individual traits on the dependence of species on historical versus current landscape configurations remains unclear. We identified the extent to which present (2000s) and historical (1843, 1954, 1980s) patch configurations (area and connectivity) and patch age affected the distributions of 99 species inhabiting dry calcareous grasslands. We used traits related to dispersal, survival, growth and habitat preferences to explain the dependence of 60 of these species on present and historical configurations, and the age of grassland patches. We found that most of the species had an affinity to currently or historically large, older and more isolated patches. This suggests that many dry grassland species are not in equilibrium with the current landscape, as their distributions still reflect past landscape structures. Rapidly growing species with higher seed bank longevity and nutrient requirements primarily occur in young, large grassland patches whereas species with the opposite traits occur in older, historically large and currently more isolated smaller patches. We hypothesise that patch quality is the reason why different species occupy patches of different age. Species occupying young, large patches commonly disperse by endozoochory. By contrast, no dispersal trait is associated with species occupying old, usually isolated patches. Our results suggest that species occupying old patches are exposed to higher potential risk of extinction, as their distributions are probably limited by the low number and connectivity of available suitable patches and poor dispersal ability. We thus suggest that the dynamics of these species can effectively be supported by improving the quality of young grassland patches.     

Hierarchical patch dynamics and animal movement pattern

In hierarchical patch systems, small-scale patches of high density are nested within large-scale patches of low density. The organization of multiple-scale hierarchical systems makes non-random strategies for dispersal and movement particularly important. Here, we apply a new method based on first-passage time on the pathway of a foraging seabird, the Antarctic petrel (Thalassoica antarctica), to quantify its foraging pattern and the spatial dynamics of its foraging areas. Our results suggest that Antarctic petrels used a nested search strategy to track a highly dynamic hierarchical patch system where small-scale patches were congregated within patches at larger scales. The birds searched for large-scale patches by traveling fast and over long distances. Once within a large-scale patch, the birds concentrated their search to find smaller scale patches. By comparing the pathway of different birds we were able to quantify the spatial scale and turnover of their foraging areas. On the largest scale we found foraging areas with a characteristic scale of about 400 km. Nested within these areas we found foraging areas with a characteristic scale of about 100 km. The large-scale areas disappeared or moved within a time frame of weeks while the nested small-scale areas disappeared or moved within days. Antarctic krill (Euphausia superba) is the dominant food item of Antarctic petrels and we suggest that our findings reflect the spatial dynamics of krill in the area.Electronic Supplementary Material Supplementary material is available to authorised users in the online version of this article at .     

Audiovisual integration in macaque face patch neurons

1. Download : Download high-res image (249KB)
2. Download : Download full-size image