Importance of Multi-Dimensional Analyses of Resource Partitioning in Highly Mobile Species Assemblages
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Popul Ecol (2015) 57:601–611 DOI 10.1007/s10144-015-0508-z ORIGINAL ARTICLE Importance of multi-dimensional analyses of resource partitioning in highly mobile species assemblages 1 1 1 Anna Roswag • Nina Inga Becker • Jorge Andre´ Encarnac¸a˜o Received: 9 December 2014 / Accepted: 25 August 2015 / Published online: 8 September 2015 Ó The Society of Population Ecology and Springer Japan 2015 Abstract Resource partitioning is an essential mecha- assessment of dietary and spatial resource partitioning in nism enabling species coexistence. The resources that are bats. used by an animal are linked to its morphology and ecol- ogy. Therefore, similar species should use similar resour- Keywords Bats Á d13C Á d15N Á Molecular diet analysis Á ces. The ecological niche of an individual summarizes all Radio telemetry used resources and is therefore composed of several dimensions. Many methods are established to study dif- ferent dimensions of an animal’s niche. The aim of this Introduction study was to demonstrate that a combination of suitable methods is needed to study spatial and dietary resource Approximately 8.7 million species coexist worldwide partitioning of sympatric species in detail. We hypothe- (Mora et al. 2011), many of them living in sympatry and sized that, while each individual method might identify sharing resources. Resource partitioning (differing resource differences between species, the combined results of sev- use of sympatric species) is a mechanism that enables the eral methods will lead to a more complete picture of spatial coexistence of species (Schoener 1974). For every species, and dietary resource partitioning. As model organisms we the ecological niche summarizes its living requirements chose the sympatric insectivorous bat species Myotis with regard to resources like habitat, diet, or environmental bechsteinii, M. nattereri, and P. auritus. We examined parameters (Townsend et al. 2008). The multi-dimensional horizontal habitat use by telemetry, vertical habitat use by nature of the ecological niche means that resource parti- measuring d13C, trophic position by measuring d15Nin tioning occurs in several dimensions (Schoener 1974). The wing membrane, and diet composition by molecular fecal most common combination of multi-dimensional resource analysis. Our results show that each method is able to partitioning is diet and habitat as suggested by Schoener provide information about spatial/dietary resource parti- (1974). Spatial segregation of species may result in the use tioning. However, considering further dimensions by of distinct foraging habitats (Pita et al. 2010) or in foraging combining several methods allows a more comprehensive at different heights (Vieira and Monteiro-Filho 2003; Voigt 2010). Dietary resource partitioning includes diet compo- sition but also trophic position within a food web (Siemers et al. 2011; Shiels et al. 2013). Spatial and dietary Electronic supplementary material The online version of this dimensions are not independent of each other as the article (doi:10.1007/s10144-015-0508-z) contains supplementary material, which is available to authorized users. availability of food resources depends on habitat charac- teristics (Townsend et al. 2008). Several methods are & Anna Roswag suitable to study spatial and dietary resource partitioning of [email protected] species. A direct method to study the habitat use of animals is radio-telemetry (Reynolds 2004; Jhala et al. 2009; Ovi- 1 Mammalian Ecology Group, Department of Animal Ecology and Systematics, Justus-Liebig-University of Giessen, dio et al. 2009; Wikelski et al. 2010). This method has the Giessen, Germany advantage that individual habitat use can be determined in 123 602 Popul Ecol (2015) 57:601–611 detail (Millspaugh et al. 2012). When applying conven- occur sympatrically (e.g., Arlettaz et al. 1997; Hillen and tional radio-telemetry, only one-dimensional habitat use Veith 2013) and, being the only actively flying mammals, can be described (Brown et al. 2009). Thus, vertical seg- occupy the three-dimensional space (Norberg and Rayner regation cannot be determined, although this factor may be 1987). Nursery colonies of European bat species are highly important for species that are able to use different heights philopatric and usually occupy the same habitats through- or depths (Wilson 2010). Overall habitat use can also be out an individual’s life (e.g., Entwistle et al. 2000; Rivers estimated indirectly by analyzing stable isotope ratios, the et al. 2006). European bats are almost exclusively insec- ratio of the heavy to the light isotope of an element (dX, tivorous (Dietz et al. 2009) feeding on several arthropod where X is the heavy isotope of the respective element). orders (Vaughan 1997). Therefore, every bat species Different isotopes may be used to test different assump- should occupy its own niche that at least slightly differs in tions. For example on a large geographical scale, hydrogen the dietary and/or spatial dimensions from that of other isotope ratios (d2H) provide insights into animal migration species. because d2H is correlated to latitude (Hobson 1999). Car- We chose the European forest-dwelling bats Myotis bon isotope ratios (d13C) are suitable to estimate foraging bechsteinii (Kuhl), Myotis nattereri (Kuhl), and Plecotus grounds (Sullivan et al. 2006) or foraging height (Voigt auritus (Linnaeus) that are very similar in their morphol- 13 2010) of animals. d C differs between C3/C4 plants and ogy and ecology (Dietz et al. 2009; Becker et al. 2013). marine/terrestrial systems (i.e., foraging grounds) and it Their nursery colonies can coexist on a very small spatial was shown for tropical forests that leaves’ d13C is corre- scale (Otto et al. 2013). All three species forage mainly lated to vegetation height (DeNiro and Epstein 1976; within deciduous forest (Entwistle et al. 1996; Kerth et al. Medina and Minchin 1980). Nitrogen stable isotopes ratios 2001; Smith and Racey 2008) and have relatively short and (d15N), are suitable to indirectly study the diet of species, broad wings with a low aspect ratio and wing loading because 15N accumulates in a characteristic way within a (Norberg and Rayner 1987). This leads to a high maneu- food web and therefore, provides information about the verability and enables them to forage within highly clut- trophic level of individuals (DeNiro and Epstein 1981). A tered space (Aldridge and Rautenbach 1987). In addition to single sample can simultaneously provide information on catching prey in flight, the three species forage by gleaning several dimensions e.g., on habitat use (d13C) and diet i.e., they collect their prey from vegetation surfaces (d15N). By choosing different tissues for analysis of stable (Neuweiler 1989; Siemers and Swift 2006). Species- isotope ratios, short (e.g., liver), intermediate (e.g., mus- specific differences in digestive efficiency (Becker et al. cle), or long (hair) time periods can be studied (MacAvoy 2012), retention times (Roswag et al. 2012), energetics et al. 2006). Stable isotope ratios in tissues always reflect a (Becker et al. 2013), and thermoregulation (Otto et al. mixed signal of all used resources (Hobson 1999) and thus 2013) are strong indicators for resource partitioning. do not allow detailed conclusions regarding individual prey This study assessed if it is possible to determine species. Morphological or molecular fecal analyses are resource partitioning in highly similar species by combin- suitable tools for studying an animal’s diet in more detail. ing stable isotope analysis, telemetry, and molecular Both techniques provide individual short-term information methods. We hypothesize that while each method might be about ingested prey items. Morphological fecal analysis able to detect differences between similar species, the can determine prey organisms only to the order or family combination of different methods will lead to a more level. While rare or highly digestible prey is often under- comprehensive picture of resource partitioning. represented, volume and proportion of the diet can be examined accurately (Whitaker et al. 2009). Molecular fecal analysis has the advantage of being able to detect Methods even rare prey organisms at the species-level (Casper et al. 2007; Razgour et al. 2011). However, no information about Study area and data collection the volume of consumed prey items is provided by this method. By a combination of several methods, strengths of The study was conducted in a small-sized (60 ha) decidu- one method can compensate the weakness of another. ous forest in Central Germany (50°270N, 8°490E). This Combining molecular fecal analysis with measurement of forest is very homogenous in its characteristics, e.g., tree d15N will, for example, provide information on prey age and species composition, and consists mainly of oak spectrum at high resolution and on the importance of dif- and beech trees. It is surrounded by orchards, agricultural ferent prey items independent of their digestibility. land, and further deciduous forests. To reduce data varia- A prerequisite for the study of resource partitioning is a tion as a result of seasonally changing environmental and stable assemblage of coexisting species. Bats (Chiroptera) physiological conditions data acquisition was limited to are suitable model organisms since several species can early pregnancy season (approximately two weeks at the 123 Popul Ecol (2015) 57:601–611 603 beginning of May). This reproduction period proceeds increase of the