Food Preferences of Winter Bird Communities in Different Forest Types

<div><p>Food availability for forest birds is a function of habitat type, forest management regime, and season. In winter, it is also impacted by variations in the weather. In the current study we assessed the food preferences of wild bird populations in two types of forest (spruce and beech) during the months of November 2010 to April 2011 in the Schwäbische Alb Biodiversity Exploratory, south-western Germany. Our aim was to investigate whether local bird communities preferred fat-rich, carbohydrate-rich or wild fruits and to determine how forest structure, seasonality and local weather conditions affected food preferences. We found higher bird activity in beech forests for the eleven resident species. We observed a clear preference for fat-rich food for all birds in both forest types. Snow cover affected activity at food stations but did not affect food preferences. Periods of extreme low temperatures increased activity.</p> </div

Temperature as measured at 10 cm above ground at each plot (within 50 m of feeding stations) during the observational hour per observation day (given in sequence from 1^st to 56^th day on <i>x</i>-axis.

<p>No data available for AEW12 for the observational period.</p

Observed activity per grouped food types during the study season from 1^st to 56^th observation day for the four grouped food types.

<p>Observed activity per grouped food types during the study season from 1^st to 56^th observation day for the four grouped food types.</p

Full generalized linear mixed effects models (Poisson) fitting activity of birds at feeding stations as response to temperature (Air temperature (min), Air temperature (max), Air temperature at 10 cm), snow cover (snow), and forest structure (Roughness, Understory, Islands, Stem Zone, Euphotic Zone, and Forest Height).

<p>Shown are the full model and all models based on AIC-scores and 95% confidence interval; model probabilities sum to 0.9.</p>a<p>as Model1 but including Food Type as fixed factor in further candidate models.</p

Summary of generalized linear mixed model fit by the Laplace approximation for full model (m1/Full Model in Table 2) with food type^a, Plot ID, Observation Hour, Species Codes, and Forest Type as random factors.

<p>Significant codes: ***: p≤0.001, **: p≤0.01, *: p≤0.05.</p>a<p>Food type was included initially as random factor but also as fixed factor in Model1.</p

Total mass, consistency, and energy content^a of food offered to the winter bird community at the Schwäbische Alb exploratory.

<p>All units in grams [g], otherwise stated.</p>a<p>Adopted from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0053121#pone.0053121-USDA1" target="_blank">[21]</a> for 100 g [02 May 2012].</p>b<p>We assigned sequence numbers for each food type on each feeding station (dish placeholder) to facilitate observations in the field.</p>c<p>Added as binding agent to prevent food disappearing from dish through wind or other incidents.</p>d<p>Lard made of pork (<i>Sus domesticus</i>).</p>e<p>Reduced mass to fit volume (not mass) of rowan into the food dishes; values adopted from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0053121#pone.0053121-Nutrition1" target="_blank">[52]</a> for 100 g.</p>f<p>Percentage of lipids <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0053121#pone.0053121-Grodziski1" target="_blank">[22]</a>.</p>g<p>Adopted from <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0053121#pone.0053121-Grodziski1" target="_blank">[22]</a>.</p

Network layers formed by interactions between ants and plants with extrafloral nectaries, trophobionts, and flowers.

<p>Circles represent plant species and diamonds represent ant species. Lines represent interactions between species and line thickness is proportional to interaction frequency. See ant and plant species codes in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0167161#pone.0167161.s001" target="_blank">S1</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0167161#pone.0167161.s002" target="_blank">S2</a> Tables, respectively.</p

Multilayer network formed by interactions between ants and plants that provide different food types.

<p>Circles represent plant species and diamonds represent ant species. Lines represent interactions and line thickness is proportional to interaction frequency. Line color represents the type of resource used. See ant and plant species names in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0167161#pone.0167161.s001" target="_blank">S1</a> and <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0167161#pone.0167161.s002" target="_blank">S2</a> Tables, respectively.</p

Few Ant Species Play a Central Role Linking Different Plant Resources in a Network in Rupestrian Grasslands

<div><p>Ant-plant associations are an outstanding model to study the entangled ecological interactions that structure communities. However, most studies of plant-animal networks focus on only one type of resource that mediates these interactions (e.g, nectar or fruits), leading to a biased understanding of community structure. New approaches, however, have made possible to study several interaction types simultaneously through multilayer networks models. Here, we use this approach to ask whether the structural patterns described to date for ant-plant networks hold when multiple interactions with plant-derived food rewards are considered. We tested whether networks characterized by different resource types differ in specialization and resource partitioning among ants, and whether the identity of the core ant species is similar among resource types. We monitored ant interactions with extrafloral nectaries, flowers, and fruits, as well as trophobiont hemipterans feeding on plants, for one year, in seven rupestrian grassland (<i>campo rupestre</i>) sites in southeastern Brazil. We found a highly tangled ant-plant network in which plants offering different resource types are connected by a few central ant species. The multilayer network had low modularity and specialization, but ant specialization and niche overlap differed according to the type of resource used. Beyond detecting structural differences across networks, our study demonstrates empirically that the core of most central ant species is similar across them. We suggest that foraging strategies of ant species, such as massive recruitment, may determine specialization and resource partitioning in ant-plant interactions. As this core of ant species is involved in multiple ecosystem functions, it may drive the diversity and evolution of the entire <i>campo rupestre</i> community.</p></div

Nonmetric multidimensional scaling ordination (NMDS) showing the similarity of most central ant species (A), and central plant species (B) among resource layers in the multilayer ant-plant network.

<p>Points represent sampling sites and the polygons indicate significant differences (EFN = ant-extrafloral nectar, Flower = ant-flower, Tropho = ant-trophobiont).</p