Habitat selection in spatially heterogeneous environments: a test of foraging behaviour in the clonal submerged macrophyte Vallisneria spiralis

1. To test whether clonal macrophytes can select favourable habitats in heterogeneous environments, clonal fragments of the stoloniferous submerged macrophyte Vallisneria spiralis were subjected to conditions in which light intensity and substratum nutrients were patchily distributed. The allocation of biomass accumulation and ramet production of clones to the different patches was examined. 2. The proportion of both biomass and ramet number of clones allocated to rich patches was significantly higher than in poor patches. The greatest values of both clone and leaf biomass were produced in the heterogeneous light treatment, in which clones originally grew from light‐rich to light‐poor patches, while clones produced the most offspring ramets in the treatments with heterogeneous substratum nutrients. Similarly, root biomass had the highest values in nutrient‐rich patches when clones grew from nutrient‐rich to nutrient‐poor patches. 3. The quality of patches in which parent ramets established significantly influenced the foraging pattern. When previously established in rich patches, a higher proportion of biomass was allocated to rich patches, whereas a higher proportion of ramet number was allocated to rich patches when previously established in poor patches. 4. Results demonstrate that the clonal macrophyte V. spiralis can exhibit foraging in submerged heterogeneous environments: when established under resource‐rich conditions V. spiralis remained in favourable patches, whereas if established in adverse conditions it could escape by allocating more ramets to favourable patches.     

Performance of a clonal species in patchy environments: effects of environmental context on yield at local and whole-plant scales

Yield of the clonal plant Glechoma hederacea was compared at different spatial scales, in heterogeneous and homogeneous environments providing the same amount of nutrients. For the heterogeneous treatments, environments were created with different patch sizes and different degrees of contrast in nutrient concentration between patches of different quality. Total clone yield differed by almost 2.5-fold across treatments, being highest in environments with large patches and high contrast, lowest in environments with small patches and high contrast, and intermediate under homogeneous conditions. Compared with plants in homogeneous conditions, there were significant increases or decreases in yield at all scales of measurement in many of the heterogeneous treatments. These effects on yield reflected a combination of local responses to growing conditions and modification of these responses due to physiological integration with other parts of the plant growing in contrasting conditions, supporting the proposal of de Kroon et al. (2005 New Phytol 166:73–82). The results show that plant yield at all scales is strongly dependent on environmental context, and that maximum yield can only be realized under a limited range of heterogeneous conditions.     

Influence of sediment fertility on morphological variability of Vallisneria spiralis L.

One homogeneous and three heterogeneous nutrient enrichment treatments were imposed to investigate the growth responses of Vallisneria spiralis L. Morphological features of V. spiralis differed significantly between different nutrient patches. Roots elongated in nutrient-poor patches, and the specific root length (SRL) also increased significantly. Stolon length, diameter and leaf length and width increased significantly in nutrient-rich patches. Total plant biomass of V. spiralis grown in the homogeneous and three heterogeneous treatments on average were 2.9, 3.0, 3.9 and 2.3 fold higher than that grown in the control treatment. Number of ramets per clone was significantly higher in the heterogeneous treatments than in the homogeneous treatment. In three varying heterogeneous treatments, ramet biomass in nutrient-rich patches was 2.7, 4.3 and 3.0 fold higher than in nutrient-poor patches; however, ramet number was not affected by sediment nutrients, resulting in bigger ramets in nutrient-rich patches. The biomass allocation established adaptive plasticity to heterogeneous environments. The maximum value of biomass allocation to underground parts reached 16% in nutrient-rich patches, whereas the minimum value of underground parts reached 20% in nutrient-poor patches. Results demonstrate that clonal V. spiralis can maintain itself preferentially in favourable nutrient-rich sediments, whereas nutrient-poor conditions could be escaped by plastic biomass allocation.     

Physiological integration helps a clonal macrophyte spread into competitive environments and coexist with other species

Physiological integration may help clonal macrophytes invade or escape from existing communities. No studies have tested the above hypothesis in aquatic plants. In an outdoor pond experiment, we subjected clonal fragments of the submerged macrophyte Vallisneria spiralis L. to heterogeneous environments in which V. spiralis spread from bare habitats towards vegetated habitats occupied by Myriophyllum spicatum L. or V. spiralis spread from vegetated habitats towards bare habitats. V. spiralis stolons between ramets in bare habitats and in vegetated habitats were either intact or severed. We investigated the habitat selection of V. spiralis by examining the allocation of biomass and ramets to heterogeneous habitats during its vegetative spread phase. Results showed that the stolon connection had different effects on the habitat selection of V. spiralis with regard to invasion and escape. When V. spiralis spread from bare to vegetated habitats, in comparison to severing the stolon, the stolon connection eventually facilitated a 49% increase in biomass and a 27% increase in number of ramets allocated to vegetated habitats. However, when V. spiralis spread from vegetated to bare habitats, biomass and ramets allocated to bare habitats were not significantly changed by the stolon connection (only a 5% increase in biomass and a 6% increase in number of ramets). These results indicate that clonal integration facilitated V. spiralis not to escape from but invade into vegetated habitats. The study provides evidence that physiological integration is important for survival and tolerance of ramets in competitively stressful environments and can help clonal macrophytes coexist with other species.     

Effects of Spatial Scale of Soil Heterogeneity on the Growth of a Clonal Plant Producing Both Spreading and Clumping Ramets

Soil nutrients are commonly heterogeneously distributed at different spatial scales. Although numerous studies have tested the effects of soil nutrient heterogeneity on growth of clonal plants producing either spreading ramets or clumping ramets, no study has examined the effects on the growth of clonal plants producing both spreading and clumping ramets and how spatial scale affects such effects. To test these effects, clones of Buchloe dactyloides, a stoloniferous clonal plant that produces both clumping and spreading ramets, were grown in six heterogeneous environments with different patch sizes and one homogeneous environment containing the same quantity of nutrients. Total biomass, total number of ramets, number of clumping ramets, number of spreading ramets, spacer length, or root:shoot ratio of the whole plants did not differ significantly among the seven treatments. However, at the patch level there were significant effects of patch size by nutrient level on biomass, number of ramets, number of spreading ramets, and number of clumping ramets, and these four variables were significantly larger in the nutrient-rich patches than in the nutrient-poor patches in the heterogeneous treatment with the largest patch size, but not in the other five heterogeneous treatments with smaller patch sizes. Neither nutrient level nor patch size significantly affected spacer length or root:shoot ratio. Based on our results, we propose that B. dactyloides can efficiently exploit nutrient-rich patches by a plastic response of clumping ramets and spreading ramets at larger spatial scales of soil heterogeneity but not at smaller ones.     

重庆中梁山不同石漠化生境中石生南亚毛灰藓斑块的空间分布格局

基于重庆市中梁山喀斯特(Karst)地区3种不同石漠化生境(潜在石漠化、轻度石漠化和中度石漠化)中0.75 hm2样地的数据,以石生南亚毛灰藓(Homomallium simlaense)的3种斑块(小斑块、中斑块和大斑块)为研究对象,运用点格局O-ring的单变量和双变量统计方法对斑块空间格局以及斑块间的关联性进行生态学特性与形成过程分析,取得以下结果。(1)南亚毛灰藓总斑块数量关系为轻度石漠化潜在石漠化中度石漠化;在3种石漠化生境中,各种类型的斑块均呈现出小斑块中斑块大斑块的数量变化。(2)小斑块和中斑块在小尺度上主要为聚集分布,其它尺度上为随机分布;大斑块在整个尺度上都呈随机分布。(3)中斑块与小斑块在3种生境中均在小尺度上有显著的关联性;大斑块与中斑块仅在潜在石漠化生境中的小尺度上有关联性,其它斑块间在不同生境与尺度上均无关联性。(4)环境因子中坡度和石缝数对斑块的分布起很大作用,但是相对湿度是影响分布的主要因子。(5)在相对湿度和郁闭度胁迫方面,小斑块和中斑块随环境胁迫增大而趋于聚集分布。研究结果表明,苔藓斑块大小及其分布式样在石漠化地区裸露岩石的生态恢复中具有重要指示意义。     

根状茎型植物扁秆荆三棱对土壤养分异质性尺度和对比度的生长响应

土壤养分的空间异质性在自然界普遍存在, 而克隆植物被认为能很好地适应和利用土壤养分异质性。尽管尺度和对比度是异质性的两个重要属性, 但有关土壤养分异质性的尺度和对比度及其交互作用对克隆植物生长和分株分布格局影响的研究仍比较缺乏。在一个温室实验中, 根状茎型草本克隆植物扁秆荆三棱(Bolboschoenus planiculmis) (异名扁秆藨草(Scirpus planiculumis))被种植在由高养分斑块和低养分斑块组成的异质性环境中。实验为两种尺度处理(大斑块和小斑块)和两种对比度处理(高对比度和低对比度)交叉组成的4种处理组合。在每个处理中, 高养分和低养分斑块的总面积相同; 在所有4种处理中, 土壤养分的总量也完全相同。无论在整个克隆(植株)水平, 还是在斑块水平, 尺度、对比度及其交互作用对扁秆荆三棱的生物量、分株数、根状茎长和块茎数的影响均不显著。然而, 在斑块水平, 扁秆荆三棱在高养分斑块中的生物量、分株数、根状茎长和块茎数均显著高于低养分斑块, 而在高养分斑块中相邻分株间的距离(间隔物长)小于低养分斑块, 并且这种效应均不依赖于斑块尺度的大小和对比度的高低。因此, 在土壤养分异质性环境中, 扁秆荆三棱可以通过缩短间隔物长, 并可能通过提高根状茎的分枝强度, 把较多的分株和潜在分株放置在养分条件好的斑块中。这种响应格局体现出克隆植物的觅食行为, 有利于整个克隆对异质性资源的吸收和利用。然而, 该实验中的尺度和对比度对扁秆荆三棱分株的放置格局均没有显著效应。作者推测, 在一个更大的斑块尺度和(或)对比度范围内, 扁秆荆三棱对土壤养分异质性的响应可能不同。因此, 下一步的研究应涉及更广泛的尺度和对比度。     

Benefits of clonal integration between interconnected ramets of Vallisneria spiralis in heterogeneous light environments

Interconnected ramets of the submersed macrophyte Vallisneria spiralis were subjected to two homogeneous treatments (shading or not shading whole plants) and two heterogeneous treatments (only shading basal or apical ramets of plants). The benefits and costs of clonal integration between connected ramets grown in heterogeneous treatments were examined. Results showed that shading apical ramets induced significant benefits to the performance of whole plant in terms of dry weight per plant (P < 0.01) and number of ramets per plant (P < 0.05). Especially for the unshaded basal ramets, their dry weight, number of ramets, number of branches and total stolon length were 89%, 30%, 29% and 58% higher than the corresponding ramets in homogeneous treatment, respectively. Compared to their controls in homogeneous treatments, unshaded basal ramets produced more leaf mass (0.15 g versus 0.11 g) whereas shaded apical ramets produced more root mass (0.012 g versus 0.008 g). However, there was a different pattern of integration when basal ramets were shaded. Shading basal ramets led to a significant decrease in stolon growth, but the individual performance of shaded ramets improved. Cost-benefit analyses revealed that dry weight per ramet of basal shaded ramets was 31% greater than that of basal shaded ramets in the homogeneous treatment. We can conclude that V. spiralis can benefit from clonal integration in heterogeneous light environments, but that the scale of these benefits is related to the quality of light environments where the clone become established.     

Biological activities as patchiness driving forces in wetlands of northern Belize

Patchiness in wetlands is a common and well documented phenomenon. Oligotrophic wetlands of northern Belize display noticeable vegetation heterogeneity at both large and small scales. In this paper, we document the small scale patches in herbaceous wetlands, describe differences between patches and surrounding wetland habitats and explain patch formation and sustenance. We conducted a survey of patches and confirmed their occurrence by spatial analysis. Patches were distinguished from a surrounding wetland by denser and taller vegetation, higher amount of empty snail shells and elevated soil phosphorus (P). Plants in patches had higher tissue nitrogen (N) and P content and there was also higher total N and P per m² incorporated in plant biomass. In terms of stable isotopes, plants in patches were enriched in ¹⁵N; patch soils were depleted in ¹³C. Observations of focal individuals of Aramus guarauna, limpkin, a wading bird feeding almost exclusively on snails, revealed the origin of the snail shell piles frequently found in patches. An adult limpkin captured on average 18 snails daily, of these 80% were handled in patches and birds often repeatedly used the same patch. Experimental patch creation by adding chicken manure or P to 1 m² plots resulted in higher and denser vegetation with values increasing in order: control, P, manure plots. The effect was significant at both experimental locations six months after the treatment and at one location even 40 months after the treatment. We present a simple mechanistic explanation for nutrient redistribution in wetlands and their eventual accumulation in patches. Both nutrient and isotopic differences result from animal input into patches, e.g. bird droppings or prey remnants. Foraging activity of Aramus guarauna is most likely responsible for patch formation. A positive feedback (repeated use of a suitable patch) is apparently the mechanism sustaining patches in these marsh environments.     

Environmental heterogeneity and clonal growth: a study of the capacity for reciprocal translocation in Glechoma hederacea L.

Clonal fragments of Glechoma hederacea L. (Lamiaceae) were subjected to environments in which light and nutrients were supplied with a strictly negative association in space, i.e. when one of these resources was in ample supply the other was scarce. Treatments were chosen to simulate environments in which clones grew either within homogeneous conditions or across patch types (heterogeneous conditions). The hypothesis was tested that reciprocal translocation (i.e. exchange of both nutrients and assimilates) between connected groups of ramets would increase biomass production of clones growing under heterogeneous conditions compared to that of clones growing in homogeneous conditions. A cost-benefit analysis was carried out to test this hypothesis. Results suggested that reciprocal translocation did not occur at the structural scale considered in this experiment; no evidence was found for a significant effect on whole clone biomass of assimilate and/or nutrient translocation between clone parts experiencing contrasting levels of resource supply. It is suggested that predominantly acropetal movement of resources and the pattern of integrated physiological unit formation in G. hederacea are the main properties responsible for the lack of mutual physiological support between connected clonal fragments growing in differing habitat conditions. These properties are expected to promote clonal expansion and the exploitation of new territory, rather than sustaining clone parts in sub-optimal patches of habitat for prolonged periods of time.     

Predation hazard and seed removal by small mammals: microhabitat versus patch scale effects

Predator avoidance may involve response strategies of prey species that are time and space specific. Many studies have shown that foraging individuals avoid predators by altering microhabitat usage; alternatively, sites may be selected according to larger-scale features of the habitat mosaic. We measured seed removal by two small mammal species (Peromyscus leucopus, and Microtus pennsylvanicus) at 474 stations over an experimentally created landscape of 12 patches, and under conditions of relatively high (full moon) and low (new moon) predatory hazard. Our objective was to determine whether predator avoidance involved the selection of small-, medium-, or large-scale features of the landscape (i.e., at the scale of microhabitats, habitats, or habitat patches). We found rates of seed removal to vary more with features of whole patches than according to variation in structural microhabitats within patches. Specific responses included: under-utilization of patch edge habitats during full moon periods, and microhabitat effects that were only significant when considered in conjunction with larger-scale features of the landscape. Individuals residing on large patches altered use of microhabitats/habitats to a greater extent than those on smaller patches. Studies just focusing on patterns of microhabitat use will miss responses at the larger scales, and may underestimate the importance of predation to animal foraging behavior.     

The effects of habitat manipulation on population distribution and foraging behavior in meadow voles

Individuals, free to choose between different habitat patches, should settle among them such that fitness is equalized. Alternatives to this ideal free distribution result into fitness differences among the patches. The concordance between fitnesses and foraging costs among inhabitants of different quality patches, demonstrated in recent studies, suggests that the mode of habitat selection and the resulting fitness patterns may have important implications to the resource use of a forager and to the survival of its prey. We studied how coarse scale selection between habitat patches of different quality and quitting harvest rate in these patches are related to each other and to fine scale patch use in meadow voles (Microtus pennsylvanicus). To demonstrate these relationships, we manipulated habitat patches within large field enclosures by mowing vegetative cover and adding supplemental food according to a 2×2 factorial design. We tracked vole population densities, collected giving‐up densities (GUDs, a measure of patch quitting harvest rate), and monitored the removal of seeds from lattice grids with 1.5 m intervals (an index of fine‐scale space use) in the manipulated habitat patches. Changes in habitat quality induced changes in habitat use at different spatial scales. In preferred habitats with intact cover, voles were despotic and GUDs were low, but increased with the addition of food. In contrast, voles in less‐preferred mowed habitats settled into an ideal free distribution, GUDs were high and uninfluenced by the addition of food. Seed removal was enhanced by the presence of cover but inhibited by supplemental food. Across all treatments, vole densities and GUDs were strongly correlated making it impossible to separate their effects on seed removal rates. However, this relationship broke down in unmowed habitats, where GUDs rather than vole density primarily influenced seed removal by voles. GUDs and seed removal correlated with predation on tree seedlings formerly planted into the enclosures, demonstrating the mechanisms between coarse‐scale habitat manipulations and community level consequences on a forager's prey.     

Hierarchical foraging by giraffe in a heterogeneous savannah,Tanzania

Understanding foraging decisions made by wildlife at different spatio‐temporal scales is important for wildlife management and conservation. We tested whether foraging decisions by Masai giraffe (Giraffa camelopardalis tippelskirchi Matschie) differed with scales; habitat, patch and tree in a heterogeneous savannah. We collected data from Arusha National Park, Tanzania, in March–May and August–October 2013. Visual observations were used to collect data on foraging behaviour. Measurements of tree height and stem height and scoring of accumulated browsing were made in 133 patches around trees where the giraffes had been seen browsing, and in a corresponding number of available patches. Giraffes selected Acacia shrub and Dodonea shrub habitats but not for water availability or predator avoidance. For patch use, giraffe selected high quantity of Acacia xanthophloea and Dodonea viscosa. Between plant species, A. xanthophloea was the most preferred and within plant species, tree quality was enhanced by tree height and high score of accumulated browsing. Generally, giraffes selected for A. xanthophloea at all scales.     

Search mechanism of a stream grazer in patchy environments: the role of food abundance

Summary The search behavior of the grazing stream insect Baetis tricaudatus (Ephemeroptera: Baetidae) was examined in field and laboratory experiments. Regardless of food abundance in experimental habitats, nymphs spent significantly more time in food patches than predicted if they had moved randomly with respect to patches. A significant reduction in movement rate within patches relative to movement rate between patches largely accounted for these results. The movement pattern within patches was highly systematic and in agreement with predictions of optimal foraging theory since food was uniformly distributed within patches. Between-patch search movements were affected by food abundance in the most recently grazed patch. Search intensity after departure from a patch was positively related to food abundance in the patch while movement rate after patch departure was inversely related to patch food level. These effects produced between-patch movement patterns that were suboptimal in the experimental habitats because they resulted in revisitation of previously depleted patches. However, differences between experimental and natural habitats in the spatial occurrence of patch types suggest that Baetis between-patch search behavior may be adaptive in natural habitats.     

Effects of flowering plant's patch size on species composition of pollinator communities,foraging strategies,and resource partitioning in bumblebees (Hymenoptera: Apidae)

Summary In 4 common Middle-European mainly bumblebee-pollinated plant species (Impatiens glandulifera, Echium vulgare, Aconitum napellus, Symphytum officinale) the influence of patch size on species composition of the pollinator community was studied. Short-tongued species were most dominant in large patches, while small patches were frequented by middle- and long-tongued bumblebees. This phenomenon was extremely obvious in Symphytum officinale and Aconitum napellus, where short-tongued species had bitten a hole in nearly every flower of large patches. Long-tongued species were forced to small patches, where nectarrobbing occurred only exceptionally. In small patches visitationrate (Number of visits per flower per hour) was not lower but either equal or even higher then in large patches. Nectar measurements in Echium vulgare showed, that not only the mean quantity of nectar but also the variance was lower in small patches. As a result, the possible gain can be predicted much more precisely in a small patch than in a large one, and bumblebees have less difficulties in making the right foraging decisions. According to this, foraging strategies depend on patch size. This was confirmed by a computer simulation. The conclusion can be drawn, that many bumblebee species are able to share the same resource by using different patch sizes. Since large flower patches occur mainly in man-made habitats, the dominance of short-tongued species in many bumblebee communities studied by other authors may be unnatural.Supported by the Landesgraduiertenförderung Baden-Württemberg     

Variable reproductive success in fragmented populations

Marine habitats are naturally patchy and anthropogenic disturbance can further fragment them. Many marine animals are sessile as adults or obligate inhabitants of particular habitats, so populations living in isolated patches of habitat are linked largely by dispersal of planktonic larvae. Theoretically, larvae are more likely to find and settle into large patches of habitat than small patches, thus small habitat patches may experience a more discontinuous supply of recruits resulting in small populations with unusual size- or age-structures or odd sex ratios — conditions where Allee effects on reproductive success are likely. We tested this hypothesis for the Caribbean spotted spiny lobster (Panulirus guttatus), an obligate inhabitant of coral patch reefs whose mating dynamics are size-dependent. We found that P. guttatus were less abundant on small reefs where their size structure and per capita reproductive success were significantly more variable, particularly among large females that are susceptible to sperm limitation that diminishes fertilization rates. These results are indicative of Allee effects and provide a mechanistic understanding of how size-dependent mating dynamics influence reproductive success in ways that alter population dynamics in patchy habitats.     

A negative heterogeneity–diversity relationship found in experimental grassland communities

Recent meta-analyses and simulation studies have suggested that the relationship between soil resource heterogeneity and plant diversity (heterogeneity–diversity relationship; HDR) may be negative when heterogeneity occurs at small spatial scales. To explore different mechanisms that can explain a negative HDR, we conducted a mesocosm experiment combining a gradient of soil nutrient availability (low, medium, high) and scale of heterogeneity (homogeneous, large-scale heterogeneous, small-scale heterogeneous). The two heterogeneous treatments were created using chessboard combinations of low and high fertility patches, and had the same overall fertility as the homogeneous medium treatment. Soil patches were designed to be relatively larger (156 cm²) and smaller (39 cm²) than plant root extent. We found plant diversity was significantly lower in the small-scale heterogeneous treatment compared to the homogeneous treatment of the same fertility. Additionally, low fertility patches in the small-scale heterogeneous treatment had lower diversity than patches of the same size in the low fertility treatment. Shoot and root biomass were larger in the small-scale heterogeneous treatment than in the homogeneous treatment of the same fertility. Further, we found that soil resource heterogeneity may reduce diversity indirectly by increasing shoot biomass, thereby enhancing asymmetric competition for light resources. When soil resource heterogeneity occurs at small spatial scales it can lower plant diversity by increasing asymmetric competition belowground, since plants with large root systems can forage among patches and exploit soil resources. Additionally, small-scale soil heterogeneity may lower diversity indirectly, through increasing light competition, when nutrient uptake by competitive species increases shoot biomass production.     

Avian seed dispersal and seedling distribution of the endangered tree species,Taxus chinensis,in patchy habitats

Background: There is limited understanding about bird dispersal behaviour and seedling distribution of endangered tree species in patchy environments, although these processes are important for plant species persistence.

Aims: We tested how patch features affected bird behaviour and seed dispersal, and thus seedling distribution of the endangered Chinese yew tree (Taxus chinensis).

Methods: In the present study, we combined field data of bird dispersal behaviour and GIS-based information to elucidate the influence of spatial features of habitat patches on bird dispersal behaviour, and the resulting effects on the seedling distribution of the endangered Chinese yew in two patchy habitats.

Results: Our results showed that the only seed source patch could attract eight bird species for dispersal at the two sites. Post-foraging movements of bird dispersers was strongly related to both topography and the relative locations of habitat patches. Yew seedlings aggregated only at the seed source and bamboo recruitment patches, which was affect by both the spatial distribution of recruitment patches and patch use by dispersers.

Conclusions: Our results emphasise that bamboo patches in both patchy environments provide the necessary conditions for germination of yew seeds, and the post-foraging behaviour of dispersers determines seed deposited in these patches. Our study highlights the importance of the dispersal behaviour of frugivorous birds in the successful regeneration and colonisation of yew populations in patchy habitats.     

Morphological responses to local light conditions in clonal herbs from contrasting habitats,and their modification due to physiological integration

Morphological responses to light and effects of physiological integration on local morphological responses are examined for Hydrocotyle vulgaris and Lamiastrum galeobdolon, stoloniferous herbs from open fenlands and forest understoreys, respectively. An assessment was made of whether these clonal herbs of similar morphology but from contrasting habitats show different foraging behaviour for light. In a garden experiment, the plants wer subjected to four levels of light availability, and to a split treatment in which the primary stolons grew along the border of patches of the two intermediate light levels. In this treatment the plant parts on opposite sides of the primary stolons were in contrasting light environments. Petiole extension was more responsive to light conditions in Hydrocotyle than in Lamiastrum, while the opposite was true for leaf area. Both species showed similar responses in stolon internode length and specific leaf area (SLA). Integration did not significantly modify local responses in stolon internode length in either species. Local responses in petiole length, leaf area and SLA of Hydrocotyle ramets were not significantly affected by physiological integration, except for the SLA of ramets in high light which was evened out by integration. In contrast, in Lamiastrum, local responses in petiole length, leaf area and SLA of many ramets in the shaded and/or light patch were significantly evened out by integration. As a result, interconnected ramets in patches of different light supply developed very different morphologies in Hydrocotyle, but not in Lamiastrum. The results indicate that the species differed in ramet morphological responses to light intensity as well as in effects of integration on local morphological responses, and suggest that species from different habitats show different foraging behaviour for light.     

Assessing habitat quality of farm-dwelling house sparrows in different agricultural landscapes

Having historically been abundant throughout Europe, the house sparrow (Passer domesticus) has in recent decades suffered severe population declines in many urban and rural areas. The decline in rural environments is believed to be caused by agricultural intensification, which has resulted in landscape simplification. We used giving-up densities (GUDs) of house sparrows feeding in artificial food patches placed in farmlands of southern Sweden to determine habitat quality during the breeding season at two different spatial scales: the landscape and the patch scale. At the landscape scale, GUDs were lower on farms in homogeneous landscapes dominated by crop production compared to more heterogeneous landscapes with mixed farming or animal husbandry. At the patch level, feeding patches with a higher predation risk (caused by fitting a wall to the patch to obstruct vigilance) had higher GUDs. In addition, GUDs were positively related to population size, which strongly implies that GUDs reflect habitat quality. However, the increase followed different patterns in homogeneous and heterogeneous landscapes, indicating differing population limiting mechanisms in these two environments. We found no effect of the interaction between patch type and landscape type, suggesting that predation risk was similar in both landscape types. Thus, our study suggests that simplified landscapes constitute a poorer feeding environment for house sparrows during breeding, that the population-regulating mechanisms in the landscapes differ, but that predation risk is the same across the landscape types.