Flower visitation by European birds offers the first evidence of interaction release in continents

Abstract

Aim All species are imbedded in a network of interactions with other species, which define an important component of their ecological niche. These interactions are dynamic and can change the emergence of vacant niches in the environment. Niche adjustments have been predicted to be particularly common on insular communities as a response to the poor and disharmonic biota of oceanic island -the interaction release hypothesis, however, the phenomena has not yet been reported on continents. Taxonomic groups of specialized nectarivorous birds are present on all continents except in Europe where they became extinct in the Oligocene, likely leaving behind underexplored flower resources. We performed the first community-level assessment of flower visitation by European birds to evaluate if insectivorous and granivorous birds show an interaction release towards consuming flower resources in Europe.Location Larc ßã -Coimbra, Portugal, Europe.Methods During one year, we collected pollen loads from the forehead of 634 birds. Pollen loads were prepared by acetolysis and all pollen grains were identified under a microscope. All interactions were compiled into a quantitative interaction matrix describing the first pollen-transport network by European birds.Results One-fifth of the bird individuals, corresponding to two thirds of the bird species sampled carried pollen from 45 different types. The vast majority of the plant species found were native but the alien Eucalyptus globulus was by far the species most commonly found in the birds' pollen loads. Overall, the structure of the pollen-transport network from Europe shared many attributes of other networks that include taxonomic groups of specialized nectarivorous birds.Main conclusions We show that the interaction release hypothesis is not exclusive to insular communities but can also be observed in continents, greatly increasing the potential geographical distribution of this phenomenon. However, it seems considerably less pronounced in Europe than in the Gal apagos, where it was first described, probably due to the much stronger selective pressures on the simplified ecosystems of oceanic islands.

Potential role of lava lizards as pollinators across the Galápagos Islands

“…Results are expressed as the percentage of samples containing at least 5 pollen grains of any plant species and as the number of pollen grains of each plant species. Fewer than 5 pollen grains of the same species was considered contamination (see Banza et al 2015;da Silva et al 2017).…”

Global patterns of the double mutualism phenomenon

“…Interaction release and niche expansion are common in island species; thus, island frugivores and insectivores, for instance, may often also consume other resources such as pollen or nectar (Traveset et al 2015), whereas presumed nectarivores have also been reported to feed on fruits (Spurr et al 2011). Interaction release in opportunistic flower-visitor bird taxa has been documented from oceanic islands (Traveset et al 2015) although, to a lesser degree, it also occurs in mainland ecosystems (da Silva et al 2017). Interaction release in opportunistic flower-visitor bird taxa has been documented from oceanic islands (Traveset et al 2015) although, to a lesser degree, it also occurs in mainland ecosystems (da Silva et al 2017).…”

“…In the Palearctic, with no nectarivorous species (da Silva et al 2017), DMs involving birds are scarce. Recent studies on bird nectarivory and pollination have sparked a wave of received attention (reviewed by da Silva et al 2014Silva et al , 2017, which may reveal more DMs in the near future. Given the importance of birds as seed dispersers for a great variety of plants in Europe (Herrera 1995), we would expect a higher frequency of DMs here.…”

“…Pollination and seed dispersal by lizards have been described as insular phenomena (Olesen and Valido 2003), and we showed that lizards are common double mutualists on islands. Interaction release in opportunistic flower-visitor bird taxa has been documented from oceanic islands (Traveset et al 2015) although, to a lesser degree, it also occurs in mainland ecosystems (da Silva et al 2017). Another, non-exclusive, explanation for the higher frequency of DMs on islands may be lower chemical defense loads in island plants due to enemy release, which results in more palatable flowers and/or fruits to a wider array of animals than in mainland areas (Bowen and Van Vuren 1997).…”

“…One example is the New Zealand honeyeater Anthornis melanura, which was the species involved in most DMs; this species is an important pollinator and seed disperser of several New Zealand plants (Anderson et al 2006), and its loss has been predicted to be detrimental to plant reproductive success (Iles and Kelly 2014). In the Palearctic, with no nectarivorous species (da Silva et al 2017), DMs involving birds are scarce. In Europe, specifically, some birds visit flowers opportunistically (da Silva et al 2014) depending upon the season (Cecere et al 2011).…”