Edge Effects in Fragmented Forests: Implications for Conservation

Article (PDF Available)inTrends in Ecology & Evolution 10(2):58-62 · February 1995with 8,982 Reads 
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DOI: 10.1016/S0169-5347(00)88977-6 · Source: PubMed
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Abstract
Edges are presumed to have deleterious consequences for the organisms that remain in forest fragments. However, there is substantial discrepancy among recent studies about the existence and intensity of edge effects. Most studies have focused on seeking simplistic and static patterns. Very few have tested mechanistic hypotheses or explored the factors that modulate edge effects. Consequently,studies are very site-specifci and their results cannot be generalized to produce a universal theory of edges. Although estimates of the intensity and impact of edge effects in fragmented forests are urgently required, little can be done to ameliorate edge effects unless their mechanics are better understood.
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  • ... Because of deforestation, 20% of the current forest area is for instance located within 100m of the forest edge (Haddad et al., 2015). While prey availability as edges may be higher because of influxes from the matrix (Debinski & Holt, 2000;Rand et al., 2006), edges are also know to show microclimatic gradients which directly affect arthropod diversity (Murcia, 1995;Schmidt et al., 2017). Warmer microclimate at forest edges, have for instance been demonstrated to favours smaller arthropods (Atkinson & Sibly, 1997;Kingsolver & Huey, 2008). ...
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    Due to physiological, behavioural or ecological mechanisms, generalist predators may show individual variation in prey consumption. This individual specialization can result from both environmental and trait variation, with especially body size strongly connected to diet. Environmental variation can thus affect consumer-predator interactions by the joint action of changes in prey community composition and predator size. We studied whether and how changes in forest environmental conditions, such as variation in tree species identity and forest fragmentation, affect predator-prey interactions. More specifically we anticipate tree diversity or spatial context to impact the predator diet directly via prey availability and prey size, but also indirectly through shifts in predator size. We used the orb-weaving spider Araneaus diadematus inhabiting forest fragments differing in edge distance, tree diversity and tree species as a model species. The species' diet was quantified by an unprecedented metabarcoding campaign. A total of 983 spiders were subjected to molecular diet analysis, from in total of 53 forest plots. A. diadematus showed to be a generalist predator, with 298 prey items detected in total. At the individual level, we found large spiders to consume less different species, but consistently larger species. Tree species composition affected both prey species richness and size in the spider's diet, although tree diversity per se had no influence on the consumed prey. Edges had an indirect effect on the spider diet as spiders closer to the forest edge were larger and therefore consumed larger prey. We attribute the structural complexity of the understory related to tree species composition as a driver of prey composition and its size distribution as reflected in the predator's diet. Although large spiders may specialize on large prey, we found no firm evidence for either ecological opportunism or strong specialization. Finally, we conclude that intraspecific size variation and tree species composition define the consumed prey of this generalist predator, and that the many feeding interactions of this spider underlie the species' success in a large diversity of habitats.
  • ... Our expectations were based on the following assumptions: (a) natural vegetation cover captures resource availability and environmental conditions that produce species occupancy (Fischer & Lindenmayer, 2007); (b) higher composition heterogeneity (diversity of land use types) increases the occurrence probability for species that use two or more vegetation types (landscape supplementation and complementation; Dunning et al., 1992); (c) Landscape supplementation and complementation also depend on landscape configuration, and are favored in patchy landscapes due to higher incidence of abrupt transitions between different land use types (edge areas; Fahrig, 2017); (d) edge areas have biotic and abiotic conditions that are different from both the matrix and the patch core region, with either positive or negative effects on species (Berl et al., 2018;Murcia, 1995); and (e) structural complexity is positively related to resource and shelter availability for both habitat patches and the matrix, and ultimately affect species movement capacity (Driscoll et al., 2013;Russel et al., 2007). ...
    Article
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    en The effects of habitat fragmentation on different taxa and ecosystems are subject to intense debate, and disentangling them is of utmost importance to support conservation and management strategies. We evaluated the importance of landscape composition and configuration, and spatial heterogeneity to explain α‐ and β‐diversity of mammals across a gradient of percent woody cover and land use diversity. We expected species richness to be positively related to all predictive variables, with the strongest relationship with landscape composition and configuration, and spatial heterogeneity respectively. We also expected landscape to influence β‐diversity in the same order of importance expected for species richness, with a stronger influence on nestedness due to deterministic loss of species more sensitive to habitat disturbance. We analyzed landscape structure using: (a) landscape metrics based on thematic maps and (b) image texture of a vegetation index. We compared a set of univariate explanatory models of species richness using AIC, and evaluated how dissimilarities in landscape composition and configuration and spatial heterogeneity affect β‐diversity components using a Multiple Regression on distance Matrix. Contrary with our expectations, landscape configuration was the main driver of species richness, followed by spatial heterogeneity and last by landscape composition. Nestedness was explained, in order of importance, by spatial heterogeneity, landscape configuration, and landscape composition. Although conservation policies tend to focus mainly on habitat amount, we advocate that landscape management must include strategies to preserve and improve habitat quality and complexity in natural patches and the surrounding matrix, enabling landscapes to harbor high species diversity. Abstract in Portuguese is available with online material. Resumo pt Os efeitos da fragmentação de habitats em diferentes taxa e ecossistemas estão sujeitos a intenso debate, e esclarecê‐los é de extrema importância para subsidiar estratégias de conservação e manejo. Avaliamos a importância da composição e configuração da paisagem em escala grossa e da heterogeneidade espacial dentro do habitat para explicar a diversidade α e β de mamíferos em um gradiente de porcentagem de cobertura de vegetação lenhosa e de diversidade de uso da terra. Esperamos que a riqueza de espécies seja positivamente relacionada a todas as variáveis explanatórias, sendo a relação mais forte com medidas de composição, com medidas de configuração da paisagem em escala grossa e com a heterogeneidade espacial dentro do habitat, respectivamente. Também esperamos que a paisagem influencie ambos os componentes da diversidade β (substituição e aninhamento), na mesma ordem de importância esperada para a riqueza de espécies, e com uma maior influência no componente de aninhamento devido à perda determinística de espécies mais sensíveis ao distúrbio no habitat. Registramos ocorrências de mamíferos de pequeno, médio e grande porte em 20 paisagens no Brasil e analisamos a estrutura da paisagem usando: (a) métricas da paisagem baseadas em mapas temáticos de cobertura da terra e (b) medidas de textura de imagem de um índice de vegetação calculadas a partir de imagens não classificadas. Comparamos um conjunto de modelos explicativos univariados de riqueza de espécies usando o Critério de Informação de Akaike e avaliamos como as diferenças entre pares de paisagens em medidas de composição e configuração da paisagem e medidas dentro de habitat de heterogeneidade espacial afetam os componentes da diversidade β usando uma regressão múltipla em uma matriz de distância. Descobrimos que, contrário às nossas expectativas, a configuração da paisagem foi o principal fator que afeta a riqueza de espécies, seguido pela heterogeneidade espacial e, por último, pela composição da paisagem. O aninhamento das espécies foi explicado, em ordem de importância, pela heterogeneidade espacial, configuração da paisagem e composição da paisagem. Embora as políticas de conservação tendem a se concentrar principalmente na quantidade de habitat, defendemos que o manejo da paisagem deve incluir estratégias para preservar e melhorar a qualidade do habitat em manchas naturais e a incrementar a complexidade da vegetação na matriz circundante, permitindo que as paisagens abriguem maior diversidade de espécies.
  • ... Entre as alterações abióticas estão pronunciados efeitos sobre o microclima, como aumento da temperatura, redução da umidade, aumento da luminosidade, aumento da exposição aos ventos e estresse hídrico. No entanto, espécies oportunistas podem beneficiar-se dessas condições e aumentar a sua densidade nessas áreas, passando a ser elemento de perturbação para a estrutura da comunidade (Murcia, 1995). ...
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    Os corredores ecológicos surgem como alternativa para mitigar os efeitos da fragmentação florestal permitindo entre eles o fluxo gênico de fauna e flora e a recolonização de áreas degradadas. Diante do exposto o presente estudo teve como objetivo, identificar para a bacia hidrográfica do rio Itapemirim, ES, por meio de metodologia desenvolvida em Sistemas de Informações Geográficas, a delimitação de corredores ecológicos que propiciem a interligação de fragmentos florestais, identificados mediante análise das métricas da paisagem como fragmentos florestais com atributos espaciais, que sugerem maior conservação. A metodologia consistiu no mapeamento dos fragmentos florestais por meio de técnicas de classificação supervisionada utilizando imagem do satélite LANDSAT 8 OLI, obtidas junto ao Instituto Nacional de Pesquisas Espaciais. Realizou-se o cálculo dos índices de ecologia, por meio do software ArcGis 10.2, com a extensão de domínio público V-LATER 2.0. Identificou-se 11.749 fragmentos florestais, que representam 22% de cobertura florestal na bacia hidrográfica. Os fragmentos pequenos (< 5 ha) foram encontrados em maior número, 8.394, seguidos pelos fragmentos de tamanho médio (5 a 50 ha), 2.995, e grandes (> 50 ha), 360. O número de fragmentos apresentaram relação inversa com sua contribuição na área. O bioma Mata Atlântica presente na bacia hidrográfica do rio Itapemirim, é representado, em sua maioria, por fragmentos florestais pequenos, menores que 5 ha, indicando um alto grau de fragmentação. Identification of Forest Fragments Potential for the delimitation of Ecological Corridors in the Itapemirim, ES River Basin through Remote Sensing techniques A B S T R A C TEcological corridors emerge as an alternative to mitigate the effects of forest fragmentation, allowing for the gene flow of fauna and flora and the recolonization of degraded areas. Given the above, the present study aimed to identify, for the Itapemirim river basin, ES, through a methodology developed in Geographic Information Systems, the delimitation of ecological corridors that allow the interconnection of forest fragments, identified through the analysis of the metrics. landscape as forest fragments with spatial attributes, which suggest greater conservation. The methodology consisted of mapping forest fragments by supervised classification techniques using LANDSAT 8 OLI satellite imagery, obtained from the National Institute for Space Research. Ecology indices were calculated using the ArcGis 10.2 software, with the public domain extension V-LATER 2.0. A total of 11,749 forest fragments were identified, representing 22% of forest cover in the watershed. Smaller fragments (<5 ha) were found in larger numbers, 8,394, followed by medium sized fragments (5 to 50 ha), 2,995, and large fragments (> 50 ha), 360. The number of fragments was inversely related to their size. contribution in the area. The Atlantic Forest biome present in the Itapemirim river basin is mostly represented by small forest fragments, smaller than 5 ha, indicating a high degree of fragmentation.Keywords: Indexes of landscape ecology, Atlantic Forest, Geoprocessing.
  • ... We believe that isolation effects in true islands are stronger than in forest fragments surrounded by a non-water matrix. Small forest remnants are associated with much stronger edge-related microclimatic effects (Murcia 1995), in which air and soil desiccation and increased solar radiation can induce high levels of larval mortality (Halffter and Edmonds 1982;Nichols et al. 2013a, b). Since the dung beetle fauna on Balbina islands are relictual populations of a previous * 30 year-old continuous matrix of undisturbed primary forest, we expected that forest loss and the creation of a water-matrix should have a much greater impact than a terrestrial matrix. ...
    Article
    The creation of mega-hydropower dams inundates vast lowland areas, causing widespread environmental impacts in tropical forest regions. Few studies, however, have taken advantage of these newly fragmented landscapes to examine the effects of habitat insularization on arthropod faunas. Here, we assess how dung beetle assemblages respond to 30 years of post-isolation history in forest islands within a major hydroelectric reservoir in Central Amazonia. We sampled 30 of the 3546 islands created by this reservoir, and three neighbouring forest sites. We collected a total of 865 individuals representing 34 dung beetle species and 15 genera. Remarkably, one third of all islands had been entirely defaunated of dung beetles in terms of overall occupancy. Isolation was the single best predictor of dung beetle species richness, followed by the interaction between isolation and island area, and these variables were key determinants of the relict species composition. Isolation was the most important predictor of dung beetle abundance, but area alone was the main predictor of abundance when the dominant species was excluded. We predicted species richness across all 3546 islands, indicating that 61.5% of all islands likely retain only a single ‘super-tramp’ species (Onthophagus osculatii). These community disassembly patterns were likely aggravated by the marked hostility of the open-water matrix combined with the poor flight dispersal capacity of dung beetles over wide gaps between insular forests. As such, the overwhelming number of small, isolated islands created by major dams has profound effects on regional forest biodiversity, including wholesale local extinctions in detritivore assemblages and their ecosystem functions.
  • ... A különböző jellegekkel rendelkező élőhelyek eltérő módon reagálhatnak az érzékenységüktől függően. Érzékeny élőhelyek lehetnek az átmeneti zónák, például az erdőssztyeppek, melyek jelentőségére már régóta felfigyeltek (Chen et al. 1993;Murcia 1995). ...
    Conference Paper
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    A globális klímaváltozás finom léptékű változásokat is okozhat. Ezek a változások az élőhelyek biotikus és abiotikus tényezőinek tér-időbeli mintázatain figyelhetők meg legkönnyebben, például a mikroklíma komponensek, a talajban mérhető háttérváltozók, a növényzet szerkezetével összefüggő, azt jellemző indexek alakulásában. Vizsgálatunkat a fülöpházi homokbuckás (Kiskunsági Nemzeti Park) egy kisebb méretű facsoportján és a közeli gyepterületen végeztük. A vegetáció-felvételezést, a változók mérését 4 különböző égtáji irányultságú, csillag alakban elrendezett szelvény mentén végeztük, melyek közepén helyezkedett el a facsoport. A szelvények mentén 0.5×0.5 m mikrocönológiai felvételeket készítettünk, illetve léghőmérsékletet, légnedvességet, talajhőmérsékletet, talajlégzést, levélfelület-indexet, tengerszint feletti magasságot mértük 2 méterenként. A gyepszintben a mikroklímát szenzor-hálózattal percenként rögzítettük. A tavaszi méréskor borult idő volt, mely nehezítette a mikroklíma komponensek jellegzetes mintázatának a detektálását. A napsütés hiányának köszönhetően a facsoport nem vetett árnyékot, így több változó mintázata csak a facsoport elhelyezkedésére és hatására vezethető vissza. A levélfelület-index térbeli ábrázolása alapján megállapítható, hogy a facsoport három egységből állt. A talajhőmérséklet és talajlégzés térbeli adatai alapján is jól kivehető a facsoport; alatta és környékén a talajhőmérséklet alacsonyabb, a talajlégzés magasabb volt. Emellett ezek jól igazodtak a domborzati viszonyokhoz is, az alacsonyabb területek hűvösségét és magasabb nedvességtartalmát is mutatták. Általánosságban a facsoport területén a Shannon-diverzitás alacsonyabb, kivéve az északi szegélyben, mert itt megtalálhatók a gyepi és facsoport alatti fajok is a nedvességviszonyoknak köszönhetően. Feltételeztük, hogy a vizsgált változók kapcsolatban vannak a lágyszárú szint határátmeneteivel. A vizuálisan meghatározott szegélyekhez viszonyítva a mikrocönológiai adatokból nyert szignifikáns folthatárok a facsoport alá húzódtak be.
  • ... Such biotic homogenization is often induced by the replacement of a diverse group of disturbance-sensitive species by a less diverse group of disturbance-adapted species that become highly prolific as anthropogenic disturbances increase (winner-loser replacement sensu Tab arelli, Peres, & Melo, 2012). Yet, our knowledge about the causal relationships between microclimate and ecological interactions remains limited, for example, despite the broad consensus that climatic alterations in species interactions, such as pollination, seed dispersal, and predation, play pivotal roles in the functional downgrading of ecosystems (Magrach, Laurance, Larrinaga, & Santamaria, 2014;Murcia, 1995). The direct responses of species interactions to climatic shifts following fragmentation, edge formation, and deforestation are surprisingly under-explored (Kelch, Neves, Fernandes, & Wirth, 2016;Patten & Smith-Patten, 2012). ...
    Article
    en The fragmentation and transformation of land cover modify the microclimate of ecosystems. These changes have the potential to modify the foraging activity of animals, but few studies have examined this topic. In this study, we investigated whether and how the foraging activity of the leaf‐cutter ant Atta cephalotes is modified by microclimatic variations due to land cover change from forest to pasture. We characterized the microclimate of each habitat and identified alterations in foraging behavior in response to relative humidity (RH), air temperature, and surface temperature along ant foraging trails by synchronously assessing foraging activity (number of ants per 5 min including incoming laden and unladen and outgoing ants) and microclimatic variables (air temperature, RH, and maximum and minimum surface temperature along the foraging trail). There were climatic differences between habitats during the day but not throughout the night, and A. cephalotes was found to have a high tolerance for foraging under severe microclimatic changes. This species can forage at surface temperatures between 17 and 45°C, air temperatures between 20 and 36°C, and an RH between 40% and 100%. We found a positive effect of temperature on the foraging activity of A. cephalotes in the pasture, where the species displayed thermophilic behavior and the ability to forage across a wide range of temperatures and RH. These results provide a mechanism to partially explain why A. cephalotes becomes highly prolific as anthropogenic disturbances increase and why it has turned into a key player of human‐modified neotropical landscapes. Abstract in Spanish is available with online material Resumen es La fragmentación y la transformación de la cobertura terrestre modifican los factores microclimáticos de los ecosistemas, Estos cambios tienen el potencial de modificar la actividad de forrajeo de los animales, pero pocos los estudios se han centrado en este tema. En este artículo, se investigó de qué manera la actividad de forrajeo de las hormigas cortadoras de hojas Atta cephalotes es afectada por las variaciones microlimáticas causadas por la transformación de bosques a pastura. Se caracterizó el microclima de cada hábitat (temperatura del aire, HR y temperatura de la superficie máxima y mínima a lo largo de los caminos de forrajeo) y sincrónicamente se midió la actividad de forrajeo (número de hormigas cada 5 minutos, incluidas las hormigas cargadas y no cargadas, entrantes y salientes). Hubo diferencias climáticas entre los hábitats durante el día, pero no durante la noche. Se encontró que A.cephalotes tiene una tolerancia alta forrajear bajo cambios microclimáticos severos. Esta especie puede forrajear cuando la temperatura de la superficie está entre 17 y 45°C, cuando las temperaturas del aire están entre 20 y 36°C y la HR entre 40 y 100%. Se encontró un efecto positivo de la temperatura sobre la actividad de forrajeo de A.cephalotes en la pastura, donde la especie mostró un comportamiento termófilo y la capacidad de forrajear en un amplio rango de temperaturas y HR. Estos resultados proporcionan un mecanismo para explicar parcialmente por qué A.cephalotes es tan prolífica a medida que aumentan las perturbaciones antropogénicas y por qué se convirtió en un agente clave en los paisajes neotropicales modificados por los humanos.
  • Thesis
    Dans le contexte du changement global et de la perte de la biodiversité, la prise en compte de cette dernière dans la gestion forestière reste encore très générale (embryonnaire). Les démarches ne sont pas encore opérationnelles alors que les gestionnaires ont besoin d'outils destinés directement à la planification. Ainsi, il est devenu urgent d'améliorer les approches d'évaluation et de suivi de la biodiversité et de développer un cadre conceptuel à partir des indicateurs biologiques qui puissent servir dans la prise de décisions. Ce travail repose sur une approche associant l'enjeu de conservation d'une espèce sauvage patrimoniale dans un paysage de montagne à la maîtrise d'une gestion forestière qui détermine la qualité de son habitat. Dans le cadre concret de la gestion forestière d'un Parc Naturel Régional où les enjeux sont multiples (écologiques, économiques, touristiques), les acteurs concernés s'interrogent moins sur le "comment gérer" que sur le "où gérer" ; en d'autres termes, définir les périmètres de bonne qualité d'habitat est nécessaire afin d'optimiser la gestion à l'échelle optimale. Notre travail est de procurer des outils aux gestionnaires et de poser les jalons scientifiques d'une approche holistique inspirée de l'écologie du paysage. Nous partons ainsi de l'hypothèse selon laquelle les variables environnementales ainsi que la structure du paysage influencent la présence d'une espèce indicatrice de la diversité biologique d'un milieu. Dans ce travail nous nous appuyons sur cette hypothèse pour développer une démarche spatialement explicite qui permettrait d'atteindre l'objectif de conservation dans le cadre d'un processus de gestion forestière adaptative, en étudiant le cas de la gélinotte des bois (Tetrastes bonasia L. 1758) dans le Parc Naturel Régional de Grande Chartreuse (Alpes françaises). Ce modèle prédictif de l'occurrence de la Gélinotte des bois en Chartreuse s'appuie sur des indicateurs environnementaux et paysagers aisément mesurables et spatialisables. Ceci permettra d'établir un diagnostic de la qualité de l'habitat, d'approfondir les connaissances sur les relations entre la structure du paysage et l'espèce à différentes échelles et de déterminer les secteurs d'habitat qui sont les plus appropriés à la Gélinotte des bois en zone de montagne. La représentation spatiale de l'hétérogénéité à différentes échelles permet d'envisager de nombreuses applications dans les domaines de la conservation et de la gestion forestière multifonctionnelle. Nos résultats, relevant d'une approche spatialement explicite, valident l'hypothèse selon laquelle la qualité de l'habitat de la Gélinotte peut être modélisée avec une précision acceptable uniquement à partir d'indices paysagers, s'ils sont calculés sur la bonne étendue. Ils constituent donc une avancée pour une aide à la gestion, puisqu'ils préfigurent un outil permettant la localisation de zones prioritaires sur lesquelles la conservation de la Gélinotte (Tetrastes bonasia) peut être optimisée.
  • Article
    Hedgerows play important roles in agricultural landscapes and they increase biodiversity by providing habitat refugia for species sensitive to agricultural disturbance. We have studied the characteristics of the communities of harvestmen (Opiliones) inhabiting hedgerows. Harvestmen are terrestrial arachnids associated with soil surface and subsurface and sensitive to land-use and disturbance. We were specifically interested in quantifying how hedgerow characteristics (e.g., elevation, length, width, connectivity, and plant diversity) affect harvestman diversity and community composition. We expected harvestman diversity and community composition to be positively related to both hedgerow size (area, length, width) and biological attributes of hedgerows (e.g., connectivity, plant community diversity). We surveyed hedgerow characteristics and harvestman communities of 20 hedgerows in an upland agricultural landscape in the Western Carpathians. Hedgerow characteristics were measured in the field or derived from GIS layers and we used correlation and ordination methods to relate them to harvestman community metrics. We found surprisingly high taxonomic richness of harvestmen within the studied hedgerows (15 species). Importantly, the Shannon index of harvestman communities was positively related to hedgerow length and hedgerow tree layer species richness and diversity. Harvestman community composition varied with hedgerow area and width. Despite their small total area, hedgerows represented an important habitat for diverse harvestman communities and hedgerow attributes such as size and tree diversity significantly affected the composition and the Shannon index of harvestman communities. Thus, greater lengths and widths of hedgerows can provide habitats for a higher Shannon index of harvestman communities, within surrounding agricultural landscapes.
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    Full-text available
    Ecotones are zones of transition between biomes or ecosystems. Ecotones, natural or anthropogenic, can greatly affect insect community structure across habitats. Scarabaeinae dung beetles are ideal biological indicators that are used to study effects of habitat modification, fragmentation and edge effects on biodiversity. Dung beetle community structure across a forest-agriculture habitat ecotone in South Western Ghats, a biodiversity hotspot in India was studied. Dung baited pitfall traps were used to collect dung beetles from forest, ecotone and agriculture habitat. Community attributes such as species richness, abundance, diversity, indicator and detector species were recorded in the study sites. Species composition varied between the three habitats. Greater similarity in species composition was observed between forest and ecotone. This is attributed to the presence of heliophilic species in the region, adapted to survive in forest and the open edge. Though forest recorded higher abundance, ecotone and agriculture habitat recorded higher species richness and diversity. Low diversity in forest resulted from decreased equitability in the overall forest assemblage resulting from increased dominance of few species such as Onthophagus furcillifer and O. pacificus. Higher species richness in ecotone and agriculture habitat was associated with heliophilic species that responded positively to disturbance, whereas stenotopic species adapted to closed canopy such as Ochicanthon mussardi was negatively affected in the region. Onthophagus furcillifer, the indicator species in the forest and ecotone was also the detector species in agriculture habitat. Presence of such species in the region that are adapted to survive in widely different habitat types is a result of decades of forest degradation and fragmentation in the Western Ghats which led to the establishment of heliophiles and synanthropic species in the region. Such increase in species richness in disturbed habitat is not considered a positive attribute, as original species composition is altered to favor disturbance adapted species in the region.
  • Technical Report
    Full-text available
    Warringah Council’s Natural Area Survey has surveyed and mapped the native vegetation of the Warringah Local Government Area outside Ku-ring-gai Chase and Garigal National Parks. The NSW Department of Environment and Climate Change has mapped the vegetation within the national parks. The present report draws on this mapping to estimate the distribution of native vegetation types in the Warringah Local Government Area prior to European settlement, for comparison with their present distribution. Maps have been produced and incorporated in Council’s geographic information system showing the distribution of the 11 native vegetation types in the Warringah Local Government Area in 1750 and 2000. A table has been compiled subdividing the 11 vegetation types into 37 vegetation communities and estimating the area of each community in 1750 and in 2000, with a further breakdown showing the reservation status of the remaining vegetation. Three additional communities have not been included in the analysis: two derived communities (not present in 1750), and a submerged aquatic community (not mapped). Forty-one percent of the native vegetation of the Warringah Local Government Area has been lost since 1750, but the impact of clearing has been very uneven. Fifteen of the 37 vegetation communities have been cleared to less than 30% of their original area. The majority of these are communities that are more or less restricted to the vicinity of the coast (within 4 km), where very little native vegetation now remains. Away from the coast, the most reduced communities are those associated with shale lenses on ridges and plateaus in Hawkesbury Sandstone. The flat topography, absence of rock outcrops, and the more fertile soils, meant that these sites were selectively cleared for agricultural and later urban development in Warringah, in preference to the rocky, rugged, infertile sandstone areas. Twenty-two of the 37 vegetation communities are poorly represented in reserves, with less than 15% of their estimated area in 1750 reserved in national parks or other reserves, or else with a reserved area of less than 5 ha. The 22 communities are: • Bangalay Slopes Forest – 10% remains, 5% reserved (8 ha reserved) • Silvertop Ash-Brown Stringybark Forest – 21% remains, 14% reserved (120 ha) • Blackbutt-Turpentine Forest – 10% remains, 1% reserved (2 ha) • Angophora-White Mahogany Forest – 100% remains (3 ha), none reserved • Coastal Banksia-Eucalypt Scrub – 7% remains, 6% reserved (10 ha) • Forest Oak Forest – 69% remains, almost all reserved, but only 2.5 ha • Tall Open-forest/Closed-forest – 69% remains, all reserved, but only 4.5 ha • Coastal Banksia-Teatree Scrub – 13% remains, almost all reserved (1.5 ha) • Narrabeen Escarpment Scrub – 34% remains, 12% reserved (1.5 ha) • Themeda Grassland – 13% remains, all reserved (0.7 ha) • Lomandra Sedgeland – 23% remains, all reserved, but only 0.2 ha • Sandstone Headland Heath – 13% remains, almost all reserved (7.5 ha) • Heart-leaved Stringybark Mallee – 68 % remains, 7% reserved (0.3 ha) • Estuarine Reedland – 16% remains, 10% reserved (5 ha) • Estuarine Paperbark Scrub – 50% remains, all reserved, but only 2.5 ha • Swamp Mahogany Forest – 16% remains, 12% reserved (4.5 ha) • Bangalay Alluvial Forest – 16% remains, 13% reserved (41 ha) • Palm Woodland – 16% remains, 9% reserved (8.5 ha) • Water Fern Swamp – 16% remains, 13% reserved (5 ha) • Paperbark Swamp – 16% remains, all reserved, but only 4 ha • Coastal Freshwater Lagoon – 100 % remains, all reserved, but only 2 ha • Coastal Dune Swamp – 1.5% remains, 1% reserved (0.5 ha) The present report also reviews the issue of wildlife corridors, core habitats and landscape connectivity. Detailed definitions and criteria are developed and are used to map core habitats and wildlife corridors in the Warringah Local Government Area, including the national parks. The mapping is based on interpretation of high definition colour air photos taken in 2008, and has been incorporated in Warringah Council's geographic information system.
  • Article
    Some ground nesting bird species, which have partially covered nests (eg Anthus trivialis, Miliaria calandra), breed close to woodland edges, whereas others, which have open nests (eg Alauda arvensis, Anthus pratensis, Motacilla flava), always breed at some distance from edges differential nest predation in relation to nest type affected nest site selection. Eggs mimicking those of skylarks were placed in open or partially covered nests at distances of 200, 25 and 0 m outside woodland edges and at distances of 25 and 100 m inside woodlots. Partially covered nest were preyed upon less often than open nests near the edge, but not at 100 m distances inside and 200 m distances outside woodlots. Magpies Pica pica preyed on open nests more often than hooded crows Corvus cornix and jays Garrulus glandarius. -from Author
  • Chapter
    Human management of the land frequently creates or sharpens landscape boundaries between natural and managed ecosystems. These boundaries often correspond approximately to natural landscape features, such as changes in slope, soil types, or riparian zones. Managed systems usually export very large fluxes of soils, nutrients, pesticides, and inorganic ions. Steep gradients of material concentrations and process rates develop across and adjacent to these boundaries. The resulting alteration in rates of processes in the natural ecosystem ultimately has secondary unanticipated effects upon soils, biota, and atmospheric exchange rates. In the below ground environment, pH, Eh, ionic composition, nutrient status, toxic metal levels, and organic matter pathways are altered. These impacts are especially important for remnant or relict natural ecosystems such as wetlands which are downslope from intensively managed ecosystems.
  • Article
    Territories of breeding forest birds in a rectangular, 21·4-ha forest plot adjacent to 800 m of a power-line corridor in East Tennessee were mapped in 1975, 1977, and 1979. Trends in density from the corridor edge to 268 m into the forest were examined for the bird community as a whole and for edge, deep forest, and unaffected species. Analysis of computer-generated, randomly distributed 'species' indicated that most trends observed in individual bird species were real. Apparently due to a tendency for some birds to establish territories in a row along the straight corridor edge, peaks in total density occurred at the edge and again in deeper forest. In each year, total density was higher at some distance into the forest than at or near the edge. The contribution of five edge species to bird density on the plot as a whole was negated by lower densities of nine deep forest species in areas near the edge. Considered as a group, thirteen forest species that individually appeared unaffected by the corridor showed a significant decrease in density with increasing distance from the corridor edge; this may have been caused by higher bird density in a small amount of mixed forest habitat near the corridor.
  • Article
    Full-text available
    In the holarctic zone many medium-sized herbivores exhibit cyclic fluctuations, which generally disappear towards the south. In Fennoscandia, cycles in abundance of tetraonid birds are found within the boreal zone but not south of it. The hypothesis that disappearance of cycles towards the south is due to increased predation pressure, predicts a gradient in predation pressure in Sweden across the border between the boreal zone and the boreo-nemoral zone. This was tested using dummy nests to measure predation pressure. As predicted, we found higher predation rate south of the border and lower predation rate north of it. The rate of predation on experimental dummy nests was correlated with the abundance of corvid birds, which in turn was positively related to the proportion of agricultural land, human density and to the degree of fragmentation of forests. /// В лоларктической области у многих фитофагов средних размеров наблюдаются циклические флуктуации, имеющие общую тенденцию к затуханию на юге. В фенноскандии циклические колебания обилия тетеревинных птиц характерны внутри бореальной зоны, но не к югу от нее. Гипотеза об исчезновении циклов на юге в результате увеличения пресса хицников предполагает наличие градиента пресса хищников в Швеции ни границе между бореальной зоной и борео-неморальной. Это проверялось путем исоользования фиктивных гнезд для оценки пресса хищников. Как и предполагалось, мы установили более высокую интенсивность хищинчества к югу от границы и более низкую - к северу от нее. Интенсивность хищничества на экспериментальных фиктивных гдездах коррдировала с обилием врановых птиц, численность котопых, в свсю очередь имеет положительныю чврзь с относительной долей сельскохозяйственных угодий, плотностью нахеления и степеныю разреженности лесов.
  • Article
    In forest, birds were relatively more common than mammals as nest robbers than in farmland. Differences in the role of different predator species as nest robbers in forest vs. farmland habitats reflected their choice of habitat. No predator seemed to have developed specific nest-robbing skills. Loss of individual nests was considered as a random event. Predation rates were higher when nests could be detected from a distance. The main factor affecting the rate of predation in patchy environments is apparently the steepness of productivity gradients between an habitat island and the surrounding matrix rather than patch size itself. -from Author
  • Article
    I used artificial nests to examine predation on birds' nests in lowland wet forest in Costa Rica. My purpose was to assess patterns of latitudinal variation in nest predation intensity and to predict the effects of further fragmentation of this forest on its associated avifauna. Nest loss did not vary among sites or between dry and wet seasons within the primary forest interior during 1988. Nests near forest/second growth edges were destroyed more frequently than nests in the forest's interior. Nest loss near forest/pasture edges, however, was similar to that in the forest interior. Nest loss was higher at five smaller (< 100 ha) than at three larger forest patches. Predation intensity at this site was comparable to that observed in three similar studies conducted in temperate forests. Comparative data from this site indicate that predation on nests of ground-dwelling birds at Barro Colorado Island, Panama, may be unusually high due to elevated densities of nest predators. High mortality rates of birds' nests previously reported for tropical forests could be an artifact of studying birds in disturbed or isolated forests.
  • Article
    We tested factors associated with predation near forest-field edge and with the ecological trap hypothesis using artificial bird nests containing Japanese quail (Coturnix japonica) eggs. Predation rates were determined for 759 nests placed in a systematic pattern within plots perpendicular to a forest-field ecotone created by commercial timber harvest in northern Idaho. One plot contained an abrupt edge and 1 contained a wide feathered edge of partial timber removal. Nests of 2 diameters (80 and 100 mm) were located on the ground and above ground in shrubs, and were placed in high- (20 nests/ha) and low-density (9 nests/ha) patterns. No difference was detected for predation rate with respect to nest location or size. Nests placed in a low-density pattern received higher percent predation than nests in a high-density pattern. The high-density plot had greater shrub cover, which may have restricted predator effectiveness. Predation rates were >4× higher in forest plots than field plots; these results may reflect relatively infrequent use of field subplots by avian predators requiring perch sites. Our data do not support the ecological trap hypothesis; we found no relationship between distance from edge and predation rate. However, our abrupt-edge subplots had higher predation than the feathered-edge subplots. These data support earlier hypotheses that birds are poorly adapted to abrupt, artificial-edge habitats, and that these habitats may have a barrier effect and create a travel lane for predators.
  • Article
    Depredation on artificial, avian ground nests in 1-ha aspen (Populus spp.) plots was studied on a ruffed grouse (Bonasa umbellus) management area in central Pennsylvania from April to July 1983. Predation was evaluated with respect to two elements of nest placement: distance from plot edge and plot age. American crows (Corvus brachyrhynchos) were the major nest predator. Avian predators rapidly associated mammalian hair-catchers, which were placed at nests to determine the identity of mammalian predators, with the location of nests. The number of total nests disturbed by predators was not related to distance of nests from edges. Nests in clear-cut plots were disturbed less by predators than those in mature plots when hair-catchers and flagging were not used at nests. The high density of small shrubs and low frequency of perch trees for avian predators in clear-cuts presumably made nests in clear-cut plots less conspicuous. Hair-catchers should not be used in studies assessing predation on nests when birds are the principal nest predators. Seasonal changes in abundance of crows, small size of plots, and relatively young age of mature plots are important factors to consider in interpreting the results of this study.