Forest remnants contribute to parasitoid conservation: experimental evaluation of parasitism on a leafminer host

The food chain length represents how much energy reaches different trophic levels in food webs. Environmental changes derived from human activities have the potential to affect chain length. We explore how habitat area and edges affect chain length through: (1) a bottom-up effect of abundance ('pyramid hypothesis'); (2) the truncation of the highest trophic level ('trophic-rank hypothesis'); and (3) changes in species connectivity patterns ('connectivity hypothesis'). We built plant-leaf miner-parasitoid food webs in 19 remnants of a fragmented Chaco forest from central Argentina. On each remnant, we constructed food webs from different locations at the forest interior and edges. For each food web, we registered the abundance of species, the species richness of each trophic level, estimated the connectivity of their networks, and the average food chain length. We used structural equation models to evaluate the direct and indirect effects of habitat area and edge/interior location on food chain length mediated by species richness, abundance and connectivity. We found no direct effects of habitat area on chain length but chains were longer at forest edges than at their interior. The three mechanisms were supported by our results, although they showed different strengths. First, we found that the interior favours a bottom-up abundance effect from herbivores to parasitoids that positively affected chain length; second, we found that the forest area positively affects plant richness, which has a strong effect on the number of resources used by consumers, with a positive effect on chain length. Third, the remnant area and interior position favoured plant richness with a negative effect on the abundance of parasitoids, which had a positive effect on chain length. In general, the strongest effects on chain length were detected through changes in abundance rather than species richness although abundance was less affected by habitat fragmentation. We evaluated for the first time the effects of human-driven habitat fragmentation on the length of trophic chains in highly diverse plant-herbivore-parasitoid networks. Despite the loss of species, small habitat fragments and edges embedded in the agricultural matrix can support interaction networks, making them conservation targets in managed landscapes.

Parasitoid assemblages infesting Yponomeuta species in the Netherlands were investigated. Parasitoid species richness and community composition were related to host species, habitat, temporal and spatial variation. Both community structure and species richness did not differ among habitats. There was no significant difference in species richness between years (1994 and 1995) but there was a significant difference in community composition. Community composition and species richness both differed among host species, although this latter result was solely due to the host species Y. evonymellus. There was no significant relationship between community similarity and distance. These results indicate that the parasitoids of the moth genus Yponomeuta in the Netherlands appear to form a spatially stable, but temporally variable community. Most of the variation in community structure was, however, related to the host species. The marked difference in parasitoid species richness and community composition of Y. evonymellus when compared to the other species warrants further study.

Small mammal assemblages in a disturbed tropical landscape at Pozuzo, Peru

Aims: The native woody vegetation from the Espinal phytogeographic province in central Argentina, found in subtropical-warm temperate climates, represents part of the southernmost seasonally dry forest in South America. Although this vegetation has been studied for over a century, a complete phytosociological survey is still needed. This lack of knowledge makes its spatial delimitation and the establishment of efficient conservation strategies particularly difficult. The main goals of this study were to classify these forests and assess their current forest cover and to better define the extent of the Espinal phytogeographic province in Córdoba region, central Argentina. Study area: Espinal Phytogeographic Province in Córdoba region, central Argentina (ca. 101,500 km2). Methods: We sampled 122 stands following the principles of the Zürich-Montpellier School of phytosociology; relevés were classified through the ISOPAM hierarchical analysis. The extent of the Espinal phytogeographic province was established by overlaying previous vegetation maps, and a map showing the current distribution of forest patches was constructed based on a supervised classification of Landsat images. Results: Four woody vegetation types of seasonally dry subtropical forest were identified based on the fidelity and the abundance of diagnostic species: (1) Aspidosperma quebracho-blanco forest; (2) Zanthoxylum coco forest; (3) Geoffroea decorticans forest; and (4) Prosopis caldenia forest. These vegetation types were segregated along gradients of temperature and precipitation seasonality and soil-texture and sodium content. The remaining forest patches represent 3.43% of the extent of the Espinal province in Córdoba region of which only 1.05% is represented in protected areas. Conclusions: We present a classification of the Espinal forest based on a complete floristic survey. Despite the dramatic forest loss reported, our results show that some forest patches representative of the Espinal are still likely to be found in the area. However, urgent measures should be taken to establish new protected natural areas in order to preserve the last remaining forest patches. Taxonomic reference: Catálogo de las Plantas Vasculares del Cono Sur (Zuloaga et al. 2008) and its online update (http://www.darwin.edu.ar). Abbreviations: ISOMAP = isometric feature mapping; ISOPAM = isometric partitioning around medoids.

Spatial and temporal isolation and environmental variability are important factors explaining variation in plant species composition. The effect of fragmentation and disturbance on woody plant species composition was studied using data from 32 remnant church forest patches in northern Ethiopia. The church forests are remnants of dry Afromontane forest, embedded in a matrix of intensively used crop and grazing lands. We used canonical correspondence analysis and partial canonical correspondence analysis to analyze the effects of fragmented and isolated forest-patch identity, environmental and spatial variables on woody plant species composition in different growth stages. The dominance of late successional species was higher at the adult growth stage than seedlings and saplings growth stages. In the adult stages, late successional species like Olea europaea subsp. cuspidate had high frequency of occurrence. Forest patch identity was more important in explaining woody plant assemblages than environmental and spatial variables. For all growth stages combined, environmental variables explained more of the explained total fraction of variation in species composition than spatial variables. Topographic variables best explained variations in species composition for saplings, adults and all growth stages combined, whereas the management regime was most important for seedlings species composition. Our results show that in a matrix of cultivated and grazing land, fragmented and isolated forest patches differ in woody plant species assemblages. Some species are widely distributed and occurred in many patches while other occurred only in one or a few forest patches. Thus, our results indicate that remnant forest patches are important for preserving rare plant species and therefore management practices should focus on minimizing disturbance to the church forests and if possible increase church forest patch size.

In the past few decades, it has been widely accepted that forest loss due to human actions alter the interactions between organisms. We studied the relationship between forest fragment size and arbuscular mycorrhizal fungi (AMF) and dark septate endophytes (DSE) colonization, and the AMF spore communities in the rhizosphere of two congeneric Euphorbia species (native and exotic/invasive). We hypothesized that these fungal variables will differ with fragment size and species status, and predicted that (a) AMF and DSE colonization together with AMF spore abundance and diversity would be positively related to forest fragment size; (b) these relationships will differ between the exotic and the native species; and (c) there will be a negative relationship between forest fragment size and the availability of soil nutrients (NH4+, NO3−, and phosphorus). This study was performed in the eight randomly selected forest fragments (0.86–1000 ha), immersed in an agricultural matrix from the Chaquean region in central Argentina. AMF root colonization in the native and exotic species was similar, and was positively related with forest fragment size. Likewise, AMF spore diversity and spore abundance were higher in the larger fragments. While DSE root colonization in the native host was positively related with forest fragment size, DSE colonization in the exotic host showed no relationship. Soil nutrients contents were negatively related with forest fragment size. In addition, NH4+ and NO3− were negatively correlated with AMF spores abundance and root colonization and with DSE colonization in the native species. The results observed in this study show how habitat fragmentation might affect the interaction between key soil components, such as rhizospheric plant-fungal symbiosis and nutrient availability. These environmental changes may have important consequences on plant community composition and nutrient dynamics in this fragmented landscape.

Urbanisation is increasing worldwide and regarded a main driver of environmental change. Urban development and associated factors like increased spatial isolation, reduced habitat size and various types of disturbances can alter the dynamics of plant and animal populations in the remaining green areas. Furthermore, changes in abiotic site conditions (e.g. temperature, moisture content) can influence habitat quality and, consequently, the species richness, species composition and functional diversity of plants and animals, which in turn can affect the functioning of ecosystems. Nonetheless, urban areas can harbour a remarkably high species richness and can be of high conservation value by serving as a refugia for many rare and threatened species. It is, therefore, of central importance in conservation biology to disentangle the various drivers of biodiversity in urban landscapes. Within the scope of this thesis, three studies were conducted to examine the consequences of urbanisation on the biodiversity and ecosystem functioning of green areas in the urban region of Basel, Switzerland.
\nThe aim of the first study was to assess the impacts of habitat size and landscape composition of the closer surroundings on the species diversity of three taxonomic groups differing in trophic rank (vascular plants, Orthoptera and Lepidoptera) in meadows and ruderal sites. I also related the response of three traits (body size, dispersal ability and food specialisation) to habitat size in Orthoptera and Lepidoptera. For this purpose, I analysed data of species from the natural heritage inventory of Basel. I found that the response of different groups of species considerably varied depending on the habitat type, taxonomic group and species trait examined. The species richness of Orthoptera and Lepidoptera was positively related to meadow size but not to the size of ruderal sites, while the opposite was true for plants. For Lepidoptera in ruderal sites, the percentage of ruderal sites in the closer surroundings was a better predictor of species richness than habitat size per se.
\nForests belong to the most frequent green areas in urban landscapes and provide a wide range of ecosystem functions and thus play a major role for human well-being in cities. The aim of the second study was to examine the potential effects of degree of urbanisation, forest size and the corresponding interaction on the species diversity and functional diversity of vascular plants, ants and spiders. The two arthropod groups do not show species-specific mutualistic or exploitative relationships with plants in contrast to those in the first study. I conducted vegetation surveys and pitfall trapping to sample soil surface-active ants and spiders. In plants, species richness decreased with the degree of urbanisation. Ants and spiders at higher trophic rank showed more pronounced shifts in species composition with increasing degree of urbanisation, while the percentage of forest specialists in both arthropod groups was positively related to forest size. Local site characteristics were also important determinants for species diversity and functional diversity. 
\nIn forests, the decomposition of leaf litter is an important component of the process of nutrient cycling and the formation of soil. In this way, litter decomposition contributes to the maintenance of several other ecosystem functions and services. The third study aimed to investigate the effects of urbanisation on leaf litter decomposition process in forests. Standardised litter of Fagus sylvatica leaves was used to assess the impact of urbanisation-related factors on the early stage of decomposition and seasonal microbial activity. I found combined effects of degree of urbanisation and forest size on the decomposition rate of leaf litter (klitter) indicating that forests of similar size differed in abiotic and biotic forest characteristics depending on the degree of urbanisation in the closer surroundings. Furthermore, moisture content of litter was the best predictor of microbial activity, followed by forest size.
\nThe findings of this thesis highlight the necessity to consider different taxonomic groups and functional groups in urban planning to maximise conservation value of urban green areas. In addition to degree of urbanisation, also habitat size was important for the diversity of some groups and leaf litter decomposition process in forests. It was also encouraging to find that even small green sites have the potential to make a significant contribution to biodiversity conservation and essential ecosystem functions in urban landscapes. I recommend that urban planners develop more flexible management strategies to satisfy the different requirements of various groups of species in the corresponding habitat type. Locally adapted management practices may provide a way forward to enhance habitat quality in a way to maximise species diversity and thus ensure the functioning of ecosystems; albeit large-scale factors also remain important.
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We evaluated puma (Puma concolor) feeding patterns in southeastern Brazilian agricultural landscapes using carbon and nitrogen stable isotope analyses of hair collected from fecal samples (N = 64). We classified the samples into three groups: feeding patterns based on forest remnants, on the agricultural matrix or both. We observed a predominance of consumption of C3prey (~47% of individuals) in the area with the highest proportion of forest coverage. Conversely, C4prey were highly consumed (~40% of individuals) where the agricultural matrix was predominant. Theδ13C values for pumas in both areas indicated that their food resources come from both forest remnants and the agricultural matrix and that some individuals preferentially consumed C4prey, indicating that food resources from the agricultural matrix make up most of their diet (~46% of prey individuals). The wide range of puma'sδ15N values in both areas indicated a diet based on different types of prey. However, the C4group had higher values, indicating that both pumas and their prey feed on enriched resources from the agricultural matrix. The results confirm the high behavioral plasticity of pumas in using highly anthropogenic habitats. The stable isotope analyses conducted in this study yielded new information on large carnivore trophic ecology that might be useful in the development of new conservation strategies in disturbed areas.

Restoration of ecosystems for biodiversity and carbon sequestration: Simulating growth dynamics of brigalow vegetation communities in Australia

Urban remnant forests are embedded in urban areas and are threatened directly and indirectly by urbanization. The direct effects (e.g., loss of area) have been well studied. However, knowledge about the indirect influence of urbanization through edge effects on the biodiversity in remnant forests is limited. In this study, we surveyed woody plant species in 72 plots in nine remnant forest patches in Guiyang, China. We examined the influences of urbanization and edge effects on the species diversity and composition of woody plants in remnant forests. We compared alpha diversities and quantified compositional dissimilarities in interior and edge sites at different levels of urbanization. We also measured the niche width of the recorded plant species and assessed whether high levels of urbanization and edge effects increased the number of generalist species. The Shannon index, the Simpson index and the Pielou index of adult trees were lowest in the edge habitat under high levels of urbanization. Significant differences in the Shannon index and the Simpson index of sapling/seedling were detected between interior and edge sites under low urbanization. The edge effects on the species composition of adult trees were intensified by high levels of urbanization. Woody plant species with wide niche widths were more abundant at edge sites under high levels of urbanization. Therefore, we recommend that urban expansion surrounding remnant patches should be strictly controlled to alleviate edge effects on biodiversity.

Widespread and rapid forest loss and disturbance have resulted in increased fragmentation of tropical forests. The impacts of forest disturbance and fragmentation on small mammals have been widely studied across the tropics and these studies have highlighted the detrimental effects. However, there is limited understanding on the impacts on small mammals in Borneo. This study investigated the impacts of fragmentation on small mammal community structure in lowland coastal heath forests known as kerangas forests, in Brunei Darussalam. Twelve study sites were compared in three forest types: fragmented (2.07-17.6 ha), disturbed (443.55-483.79 ha) and undisturbed (>500 ha) forests. In addition, the correlations between species richness, abundance and biomass of small mammals, and forest size were investigated. There was a clear change in species composition in the different forest types. Fragmented forests had the lowest species richness but the highest pooled abundance and biomass compared with disturbed and undisturbed forests. Species richness increased with forest size as predicted by the theory of island biogeography. In contrast, abundance and biomass was negatively correlated to forest size. Factors that contribute to the pronounced decline in species richness in fragmented forests include loss of rare and native forest species, reduced forest size in fragmented forests and distance effect. We suggest that a release from top-down control by predators and favourable conditions as a result from forest fragmentation are responsible for higher abundance and biomass of small mammals in fragmented forests.

Research Highlights: Variations in species composition across church forests in northern Ethiopia were driven more by variations in human disturbance and community forest management than forest size. The degree of human disturbance acted as an environmental filter that selected for weedy, exotic, and wind-dispersed species regardless of forest size. Background and Objectives: Forest fragmentation can profoundly influence the long-term persistence of forests on the landscape. Habitat fragmentation can increase edge effects and limit dispersal between forest patches. In the South Gondar Administrative Zone in northern Ethiopia, many of the remaining forests are small sacred church forests governed by the Ethiopian Orthodox Tewahido Church. Materials and Methods: We examined the drivers of woody plant species composition across 46 church forests in this region, including the influence of elevation, forest size, distance between forests, human disturbance, the presence of a wall, and the importance of local/individual community forest management at the Woreda level. We also examined how dispersal syndromes are influenced by increasing distance between forests and the extent of human disturbance within forests. Results: We found that elevational zone, distance between forests, the degree of human disturbance and Woreda had the greatest effect on species composition. Forest size and the presence of a wall were not significant drivers of species composition in these forests. Conclusions: We propose connecting forests through corridors or scattered trees to increase dispersal between forests, and greater on-the-ground protection efforts to restrict people and cattle from leaving the main trails within sacred forests

Urbanisation is increasing worldwide and is regarded a major driver of environmental change altering local species assemblages in urban green areas. Forests are one of the most frequent habitat types in urban landscapes harbouring many native species and providing important ecosystem services. By using a multi-taxa approach covering a range of trophic ranks, we examined the influence of degree of urbanisation and forest size on the species richness and functional diversity of plants, and ground surface-active ants and spiders. We conducted field surveys in twenty-six forests in the urban region of Basel, Switzerland. We found that a species’ response to urbanisation varied depending on trophic rank, habitat specificity and the diversity indices used. In plants, species richness decreased with degree of urbanisation, whereas that of both arthropod groups was not affected. However, ants and spiders at higher trophic rank showed greater shifts in species composition with increasing degree of urbanisation, and the percentage of forest specialists in both arthropod groups increased with forest size. Local abiotic site characteristics were also crucial for plant species diversity and species composition, while the structural diversity of both leaf litter and vegetation was important for the diversity of ants and spiders. Our results highlight that even small urban forests can harbour a considerable biodiversity including habitat specialists. Nonetheless, urbanisation directly and indirectly caused major shifts in species composition. Therefore, special consideration needs to be given to vulnerable species, including those with special habitat requirements. Locally adapted management practices could be a step forward to enhance habitat quality in a way to maximize diversity of forest species and thus ensure forest ecosystem functioning; albeit large-scale factors also remain important.

Abstract. 1. Associational resistance theory suggests that the association of herbivore-susceptible plant species with herbivore-resistant plant species can reduce herbivore density on the susceptible plant species. Several casual mechanisms are possible but none has so far invoked natural enemies. Associational resistance mediated by natural enemies was tested for by examining densities of a gall fly, Asphondylia borrichiae (Diptera: Cecidomyiidae), and levels of parasitism on two closely related seaside plants, Borrichia frutescens and Iva frutescens, when alone and when co-occurring. 2. Both Borrichia and Iva grow alone or together on small offshore islands in Florida. Each host plant species has its own associated race of fly, but both races of fly are attacked by the same four species of parasitoids. Borrichia normally has a higher density of galls than Iva, and galls are larger on Borrichia than on Iva. 3. Gall size, gall abundance, parasitism levels, and parasitoid community composition were quantified on both Borrichia and Iva on islands where each species grew alone or together. Some islands were then manipulated by adding Borrichia to islands supporting only Iva, and by adding Iva to islands supporting only Borrichia. Subsequent gall densities and gall parasitism levels on the original native species were then examined. 4. On both natural and experimentally manipulated islands, gall densities on Iva were significantly lowered by the presence of Borrichia. This is because bigger parasitoid species that were common on Borrichia galls, which are bigger, spilled over and attacked the smaller Iva galls. Thus, parasitism rates on Iva were higher on islands where Borrichia co-occurred than on islands where Borrichia were absent. Most parasitoids from Iva were too small to successfully attack the large Borrichia galls and so gall density on Borrichia was unaffected by the presence of Iva.

We studied reproductive parameters, agonistic interactions, foraging behavior, prey deliveries, and diet of American Kestrels (Falco sparverius) using nest boxes in semiarid forests in central Argentina. The breeding season (from egg-laying to fledging) began in late October and ended in late December. Average clutch size was 4.3 ± 0.3 (SE) eggs (N = 6 nests), hatching success was 73%, and nest success was 66%. Incubation was primarily by females, whereas males mostly hunted and defended the nest area. During early and late nestling stages, both sexes showed aggressive behavior against intruders. The primary hunting method we observed kestrels using near the nest box was perch-hunting (99%), with a peak in hunting activity during midday for females and during morning for males. Both sexes visited the nest most frequently during the late nestling stage (males: 1.04 ± 0.47 prey/hr; females: 1.22 ± 0.35 prey/hr), likely because of high energy demands of the nestlings for growth during that time. The majority of the nestling diet was arthropods (71.4% of diet as determined by observations; 71% by pellets; 89% by prey remains). Reproductive characteristics of this species in the semiarid forest of central Argentina, including reproductive rate, role partitioning between sexes, foraging behavior, and diet, are similar to those previously recorded for some populations in North America.