Experimental Evidence for the Population-Dynamic Mechanisms Underlying Extinction Cascades of Carnivores

SummarySpecies extinction rates due to human activities are high [1–3], and initial extinctions can trigger cascades of secondary extinctions, leading to further erosion of biodiversity [4]. A potential major mechanism for secondary extinction cascades is provided by the long-standing theory that the diversity of consumer species is maintained due to the positive indirect effects that these species have on each other by reducing competition among their respective resource species [5–7]. This means that the loss of one carnivore species could lead to competitive exclusion at the prey trophic level, leading to extinctions of further carnivore species. Evidence for these effects is difficult to obtain due to many confounding factors in natural systems, but extinction cascades that could be due to this mechanism have been demonstrated in simplified laboratory microcosms [8]. We established complex insect food webs in replicated field mesocosms and found that the overharvesting of one parasitoid wasp species caused increased extinction rates of other parasitoid species, compared to controls, but only when we manipulated the spatial distribution of herbivore species such that the potential for interspecific competition at this level was high. This provides clear evidence for horizontal extinction cascades at high trophic levels due to the proposed mechanism. Our results demonstrate that the loss of carnivores can have widespread effects on other species at the same trophic level due to indirect population-dynamic effects that are rarely considered in this context

Impacts of fire and prospects for recovery in a tropical peat forest ecosystem

Uncontrolled fires place considerable burdens on forest ecosystems, compromising our ability to meet conservation and restoration goals. A poor understanding of the impacts of fire on ecosystems and their biodiversity exacerbates this challenge, particularly in tropical regions where few studies have applied consistent analytical techniques to examine a broad range of ecological impacts over multiyear time frames. We compiled 16 y of data on ecosystem properties (17 variables) and biodiversity (21 variables) from a tropical peatland in Indonesia to assess fire impacts and infer the potential for recovery. Burned forest experienced altered structural and microclimatic conditions, resulting in a proliferation of nonforest vegetation and erosion of forest ecosystem properties and biodiversity. Compared to unburned forest, habitat structure, tree density, and canopy cover deteriorated by 58 to 98%, while declines in species diversity and abundance were most pronounced for trees, damselflies, and butterflies, particularly for forest specialist species. Tracking ecosystem property and biodiversity datasets over time revealed most to be sensitive to recurrent high-intensity fires within the wider landscape. These megafires immediately compromised water quality and tree reproductive phenology, crashing commercially valuable fish populations within 3 mo and driving a gradual decline in threatened vertebrates over 9 mo. Burned forest remained structurally compromised long after a burn event, but vegetation showed some signs of recovery over a 12-y period. Our findings demonstrate that, if left uncontrolled, fire may be a pervasive threat to the ecological functioning of tropical forests, underscoring the importance of fire prevention and long-term restoration efforts, as exemplified in Indonesia

Plant-modified trophic interactions

Copyright © 2015 Elsevier Inc. All rights reserved.Plants can modify the interactions between herbivorous insects and their natural enemies in various ways. Chemical defences from the plants against herbivores may in fact harm the latter's natural enemies, thereby weakening the trophic interaction. On the other hand, volatile chemicals produced by the plant in response to herbivory may attract natural enemies, thereby strengthening the interaction. Recent research shows that effects of plants on insect interactions are not curious phenomena confined to a few specialist species but rather that they are ubiquitous in terrestrial ecosystems and often involve complex interactions among many species. The major challenge now is to study how the commonly reported short-term effects of plants affect long term dynamics of insect interactions in the context of complex natural communities.NER

Response of avian diversity to habitat modification can be predicted from life-history traits and ecological attributes

AcceptedArticle in PressCopyright © 2015 Springer International Publishing AG, Part of Springer Science+Business MediaContext: Habitat conversion for agriculture is a major driver of global biodiversity loss, partly because of homogeneity within agri-ecosystems. Anthropogenic landscapes can also increase habitat heterogeneity and primary productivity, however, augmenting regional biodiversity, as species that exploit resources associated with human activities expand their ranges into novel ecological regions.European Commission Marie Curie International Research Staff Exchange Scheme (IRSES)DST Financial Assistance agreementNR

Conformationally flexible calix[4]arene chromoionophores: optical transduction of soft metal ion complexation by cation-pi interactions

Self-assembled monolayers (SAMs) of crown ether adsorbates on gold reversibly bind metal ions from aqueous solutions. The resulting changes of the electrochemical properties of the monolayers were monitored by impedance spectroscopy. The increased dielectric constant of the layer due to the complexation of ions results in an increase of the monolayer capacitance (CML). Analysis of the response curves with a Langmuir isotherm enables the determination of association constants of the SAMs with various metal ions. The cation binding also influences the charge-transfer resistance (RCT) of a redox couple Ru(NH3)62+/3+ in the electrolyte. Comparison of both responses allows an accurate interpretation of the origin of the resistive response. Furthermore, the association constants enable the quantitative determination of interactions between SAMs and metal ions, using either capacitive or resistive responses

Natural vegetation benefits synergistic control of the three main insect and pathogen pests of fruit crop in southern Africa

Copyright © 2015 The Authors. Journal of Applied Ecology © 2015 British Ecological Society1 Most studies of the potential for natural habitat to improve agricultural productivity have been conducted in transformed, temperate regions, but little is known of the importance of agroecosystem services in biodiverse developing countries. 2 Natural vegetation may promote the density and/or diversity of natural enemies of crop pests, but the strength of the effect varies, and few studies directly measure concurrent impacts on pest density. Considering multiple pest species within the same agroecosystem may help explain why some pests are more affected than others by landscape complexity. Here, we investigated multiple pest species (leaf-galling flies, three species of Tephritidae fruit fly and pathogenic fungi Fusarium spp.) and their enemies in cultivated mango Mangifera indica, in North-Eastern South Africa. 3 The density of generalist Tephritidae fruit flies increased with distance from natural vegetation during harvesting months, and predation rate of pupae sharply decreased from ~50% at the edge with natural vegetation to 0% at 250m into the crop. Parasitism rates of the cryptic, gall-forming fly increased with proximity to natural vegetation but pest density was unrelated to distance from natural vegetation. Incidence of the fungal pathogen disease increased with distance from natural vegetation, possibly due to decreased predation of commensal mites. 4 Although the relationship with distance to natural vegetation was significant for all species considered, the strength of this relationship varied across pest species and type of natural enemy studied, suggesting the benefits of natural vegetation depends on each natural enemy species’ ability to disperse into the agricultural environment. 5 Syntheses and applications. Our results suggest that natural vegetation is a net source of natural enemies in a region of South Africa that still contains much of its natural biodiversity. However, the decline in natural enemies, and increase in pests, with distance from natural habitat indicates that this biocontrol is limited by natural enemy dispersal. In landscapes like these that are still dominated by natural habitat, conservation biocontrol can still be improved by management aimed at providing corridors of key plants and habitat elements into to the crops, to facilitate natural enemy dispersal.European Commission Marie Curie Programme International Research Staff Exchange Scheme (IRSES).South African Department of Science and TechnologyNRF of South AfricaNER

Data from: Crop pests and predators exhibit inconsistent responses to surrounding landscape composition

The idea that noncrop habitat enhances pest control and represents a win–win opportunity to conserve biodiversity and bolster yields has emerged as an agroecological paradigm. However, while noncrop habitat in landscapes surrounding farms sometimes benefits pest predators, natural enemy responses remain heterogeneous across studies and effects on pests are inconclusive. The observed heterogeneity in species responses to noncrop habitat may be biological in origin or could result from variation in how habitat and biocontrol are measured. Here, we use a pest-control database encompassing 132 studies and 6,759 sites worldwide to model natural enemy and pest abundances, predation rates, and crop damage as a function of landscape composition. Our results showed that although landscape composition explained significant variation within studies, pest and enemy abundances, predation rates, crop damage, and yields each exhibited different responses across studies, sometimes increasing and sometimes decreasing in landscapes with more noncrop habitat but overall showing no consistent trend. Thus, models that used landscape-composition variables to predict pest-control dynamics demonstrated little potential to explain variation across studies, though prediction did improve when comparing studies with similar crop and landscape features. Overall, our work shows that surrounding noncrop habitat does not consistently improve pest management, meaning habitat conservation may bolster production in some systems and depress yields in others. Future efforts to develop tools that inform farmers when habitat conservation truly represents a win–win would benefit from increased understanding of how landscape effects are modulated by local farm management and the biology of pests and their enemies