Jens M Olesen

Jens M Olesen
Aarhus University | AU · Department of Bioscience

PhD, MSc, MHortonomy
Professor emeritus, ecology

About

224
Publications
104,394
Reads
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19,856
Citations
Introduction
Island ecology (sub-Antarctic Islands, Canaries, Caribbean Islands), new network types and structures.
Additional affiliations
January 1990 - present
Aarhus University
Position
  • Professor (Full)

Publications

Publications (224)
Article
Full-text available
Species in ecological communities build complex webs of interaction. Although revealing the architecture of these networks is fundamental to understanding ecological and evolutionary dynamics in nature, it has been difficult to characterize the structure of most species-rich ecological systems. By overcoming this limitation through next-generation...
Article
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Owing to food scarcity and to the high densities that vertebrates often reach on islands, typical insect- and seed-eaters widen their feeding niche and interact with a greater fraction of species than their mainland counterparts. This phenomenon, coined here ‘interaction release’, has been previously reported for single species but never for an ent...
Article
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A recurrent concern in nature conservation is the potential competition for forage plants between wild bees and managed honey bees. Specifically, that the highly sophisticated system of recruitment and large perennial colonies of honey bees quickly exhaust forage resources leading to the local extirpation of wild bees. However, different species of...
Preprint
Full-text available
The importance of keystone species is often defined based on a single type of interaction (e.g., keystone predator). However, it remains unclear whether this functional importance extends across interaction types. We conducted a global meta-analysis of interaction networks to examine whether species functional importance in one niche dimension is m...
Article
Bees (Apoidea) are the main pollinator group in Mediterranean ecosystems, having a dominant role as connectors of modules (groups of species tightly linked in pollination networks), but little is known about the role of particular species. Here, we analyse data from four Iberian networks, and we pay special attention to the role played by the solit...
Article
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Despite it is widely accepted that intra-population variation is fundamental to ecological and evolutionary processes, this level of information has only recently been included into network analysis of species/population interactions. When done it has revealed non-random patterns in the distribution of trophic resources. Nestedness in resource use...
Article
Fern sporangia may provide an important source of energy for bird species, which in turn can act as potential dispersers of viable spores. This study reports the first case of fern spore dispersal by land birds. We document the consumption of fern sporangia and evaluate the potential spore dispersal by Galápagos Finches on Santa Cruz Island. Overal...
Article
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Birds and mammals are the only vertebrates which receive comprehensive attention in studies of dispersal of fleshy-fruited plant species. However, recently the importance of fleshy fruit in the diet of lizards (order Squamata: suborder Sauria), and their role as seed dispersers have been recognized in a number of studies, especially in studies from...
Article
Lizards have been reported as important pollinators on several oceanic islands. Here we evaluate the potential role of Galápagos lava lizards (Microlophus spp.) as pollinators across their radiation. During three years, we sampled pollen transport by nine lava lizard species on the 10 islands where they are present, including seven single‐island en...
Article
PREMISE OF THE STUDY: The characteristic scarcity of insects on remote oceanic islands has driven non-flower specialized vertebrates to broaden their trophic niches and explore floral resources. From our previous studies in the Galápagos, we know that native insectivorous and frugivorous birds visit a wide range of entomophilous flowers and can als...
Article
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A striking structural pattern of pollination networks is the presence of a few highly connected species which has implications for ecological and evolutionary processes that create and maintain diversity. To understand the structure and dynamics of pollination networks we need to know which mechanisms allow the emergence of highly connected species...
Article
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A double mutualism (DM) occurs when two interacting species benefit each other in two different functions, e.g. when an animal species acts both as pollinator and seed disperser of the same plant. Besides the double benefit, a DM also imposes a larger risk to both functions if the performance of one partner declines. We conducted the first global r...
Article
As hunters and gatherers, humans have always exploited a wide variety of natural resources. Hunting, in particular, focuses upon individual species.The relationships between human and game are most often seen as isolated entities, for example, human–bison, human–whale, human–seabird or human–mammoth. However, hunting interactions are embedded in la...
Article
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Frugivory in lizards is often assumed to be constrained by body size; only large individuals are considered capable of consuming fruits, with the potential of acting as seed dispersers. However, only one previous study has tested the correlation of frugivory with body and head size at an archipelago scale across closely related species. All nine la...
Article
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Network approaches to ecological questions have been increasingly used, particularly in recent decades. The abstraction of ecological systems – such as communities – through networks of interactions between their components indeed provides a way to summarize this information with single objects. The methodological framework derived from graph theor...
Article
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Despite progress in understanding pollination network structure, the functional roles of floral sensory stimuli (visual, olfactory) have never been addressed comprehensively in a community context, even though such traits are known to mediate plant-pollinator interactions. Here, we use a comprehensive dataset of floral traits and a novel dynamic da...
Data
The weighted plant-pollinator interactions network including 41 plant and 168 insect species, recorded in a Mediterranean scrubland (phrygana) in Lesvos Island, Greece.
Data
Inflorescence volatile compounds of the plant species studied.
Article
In recent years, as economic globalization and long-distance trade have increased, so has the unintentional transport of non-human species. During the past 30 years, the species diversity of harvestmen (Opiliones) in northern Europe has changed dramatically due to the arrival of new species from southern Europe. Here we explore the changing harvest...
Article
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Inter-annual turnover in community composition can affect the richness and functioning of ecological communities. If incoming and outgoing species do not interact with the same partners, ecological functions such as pollination may be disrupted. Here, we explore the extent to which turnover affects species’ roles – as defined based on their partici...
Article
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Life on oceanic islands deviate in many ways from that on the mainland. Their biodiversity is relatively poor and some groups are well-represented, others not, especially not insects. A scarcity of insects forces birds to explore alternative food, such as nectar and fruit. In this way, island birds may pollinate and disperse seed to an extent unsee...
Article
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For hundreds of millions of years, large vertebrates (megafauna) have inhabited most of the ecosystems on our planet. During the late Quaternary, notably during the Late Pleistocene and the early Holocene, Earth experienced a rapid extinction of large, terrestrial vertebrates. While much attention has been paid to understanding the causes of this m...
Article
Angiosperm flowers have evolved a dazzling palette of colours and a rich bouquet of scents, principally serving to attract pollinators. Despite recent progress in the ecology of pollination, the sensory floral traits that are important for communication with pollinators (for example, colour and scent) have not been assessed in an unbiased, integrat...
Article
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The general dynamic model of oceanic island biogeography (GDM) has added a new dimension to theoretical island biogeography in recognizing that geological processes are key drivers of the evolutionary processes of diversification and extinction within remote islands. It provides a dynamic and essentially non-equilibrium framework generating novel p...
Article
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1. The ongoing biodiversity crisis entails the concomitant loss of species and the ecological services they provide. Global defaunation, and particularly the loss of frugivores, may negatively affect the seed dispersal of fleshy-fruited plant species, with predictable stronger impacts in simplified communities such as those on oceanic islands. Howe...
Article
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Networks provide one of the best representation for ecological communities, composed of many speecies with dense connections between them. Yet the methodological literature allowing one to analyse and extract meaning from ecological networks is dense, fragmented, and unwelcoming. We provide a general overview to the field, outlining both the intent...
Article
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Seed dispersal and seedling recruitment are crucial phases in the life cycle of all spermatophyte plants. The net contribution of seed dispersers to plant establishment is known as seed dispersal effectiveness (SDE) and is defined as the product of a quantitative (number of seeds dispersed) and a qualitative (probability of recruitment) component....
Article
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Land degradation results in declining biodiversity and the disruption of ecosystem functioning worldwide, particularly in the tropics. Vegetation restoration is a common tool used to mitigate these impacts and increasingly aims to restore ecosystem functions rather than species diversity. However, evidence from community experiments on the effect o...
Article
Understanding how ecological and evolutionary processes interdependently structure biosphere dynamics is a major challenge in the era of worldwide ecosystem degradation. However, our knowledge of ‘eco-evolutionary feedbacks’ depends largely on findings from simple systems representing limited spatial scales and involving few species. Here we review...
Article
To assess the spatial congruence between hotspots based on taxonomic, phylogenetic and functional diversity, after accounting for the correlation between diversity metrics, and the spatial scale and sampling completeness of data. The Ordesa and Monte Perdido National Park (Central Pyrenees, Spain), a species-rich area subjected to intensive botanic...
Article
Mutualistic network parameters, such as modularity and nestedness, show non-random linkage patterns. Both increase network stability in different ways. Modularity hampers extinction cascades, whereas nestedness resists network disassembly. We explore these parameters in seed-dispersal networks in two archipelagos and the significance of life histor...
Article
1.There has been an intense focus on the response of species to environmental changes and more recently the interactions of species have been examined in a similar way in order to understand the stability of entire communities and networks of interacting species. As a consequence, ecological networks have been placed in spatial and temporal context...
Article
Island organisms often have wider feeding niches than mainland organisms, and migratory birds breeding on continents often widen their niches when overwintering on islands. Cuba’s low hummingbird richness has puzzled ornithologists for decades. Here, we show that the Cuban hummingbird fauna is less rich than expected based on Cuba’s elevation, when...
Article
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The foundational concepts behind the persistence of ecological communities have been based on two ecological properties: dynamical stability and feasibility. The former is typically regarded as the capacity of a community to return to an original equilibrium state after a perturbation in species abundances, and is usually linked to the strength of...
Article
Seed dispersal, together with pollination, are two key services provided by animals to plants. On oceanic islands, where strong isolation limits the arrival of medium and large sized mammals (Gorman 1979), tortoises, iguanas or lizards often undertake an important ecological role as dispersers (Olesen & Valido 2003). Furthermore, the reported niche...
Article
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In nature, plants and their pollinating and/or seed-dispersing animals form complex interaction networks. The commonly observed pattern of links between specialists and generalists in these networks has been predicted to promote species coexistence. Plants also build highly species-rich mutualistic networks below ground with root-associated fungi,...
Article
AimInteraction networks are being increasingly used to evaluate macroecological patterns. We explored a global dataset to identify differences in the structure of pollination networks from islands (of oceanic and continental origin) and mainlands. For oceanic islands, we further evaluated the effects of key island traits on network structural param...
Article
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Oceanic archipelagos are threatened by the introduction of alien species which can severely disrupt the structure, function and stability of native communities. Here we investigated the pollination interactions in the two most disturbed Galápagos Islands, comparing the three main habitats and the two seasons, and assessing the impacts of alien plan...
Article
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Although species and their interactions in unison represent biodiversity and all the ecological and evolutionary processes associated with life, biotic interactions have, contrary to species, rarely been integrated into the concepts of spatial β-diversity. Here, we examine β-diversity of ecological networks by using pollination networks sampled acr...
Article
Most flowering plants depend on animal pollination. Several animal groups, including many birds, have specialized in exploiting floral nectar, while simultaneously pollinating the flowers they visit. These specialized pollinators are present in all continents except Europe and Antarctica, and thus, insects are often considered the only ecologically...
Article
Downscaling networks from species to individuals is a useful approach to incorporate inter-individual variation and to investigate whether topology of species-based networks results from processes acting at the scale of individuals, such as foraging behaviour. Here, we analyzed pollen-transport networks at two scales, i.e. pollinator species–plant...
Chapter
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Oceanic islands provide a good model for the study of species dispersal and evolution. We focus here on the evolution of pollination modes of oceanic island bellflowers (Campanulaceae), examining the degree of parallel evolution in different lineages of this family. Plants colonizing islands might either have experienced selective pressures on flor...
Article
The influence of space on the structure (e.g. modularity) of complex ecological networks remains largely unknown. Here, we sampled an individual-based plant–pollinator network by following the movements and flower visits of marked bumblebee individuals within a population of thistle plants for which the identities and spatial locations of stems wer...
Article
A new approach for investigating evidence for the capacity of plant colonization between islands and the success of plant morphological traits associated with seed dispersal is presented. As colonization is the result of dispersal and establishment, oceanic archipelagos provide an ideal spatio-temporal system in which to analyse plant dispersal tra...
Article
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In recent years, the analysis of interaction networks has grown popular as a framework to explore ecological processes and the relationships between community structure and its functioning. The field has rapidly grown from its infancy to a vibrant youth, as reflected in the variety and quality of the discussions held at the first international symp...
Article
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Most ecological networks are analysed as static structures, where all observed species and links are present simultaneously. However, this is over-simplified, because networks are temporally dynamical. We resolved an arctic, entire-season plant-flower visitor network into a temporal series of 1-day networks and compared the properties with its stat...