Scale Distribution of Springtails (Collembola) 1, 2 1 3 LINA A
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Age and level of self-organization affect the small-scale distribution of springtails (Collembola) 1, 2 1 3 LINA A. WIDENFALK , HANS PETTER LEINAAS, JAN BENGTSSON, AND TONE BIRKEMOE 1Department of Ecology, Swedish University of Agricultural Sciences, P.O. Box 7044, Uppsala, SE-75007 Sweden 2Department of Biosciences, University of Oslo, P.O. Box 1066, Blindern, Oslo, N-0316 Norway 3Faculty of Environmental Sciences and Natural Resource Management, Norwegian University of Life Sciences, P.O. Box 5003, As, NO 1432 Norway Citation: Widenfalk, L. A., H. P. Leinaas, J. Bengtsson, and T. Birkemoe. 2018. Age and level of self-organization affect the small-scale distribution of springtails (Collembola). Ecosphere 9(1):e02058. 10.1002/ecs2.2058 Abstract. In studies of community assembly, species are often assumed to have similar spatial distribu- tions and responses to the environment regardless of age or size. Under this assumption, it is possible to use species and species-level traits in community composition studies. Here, we test this assumption for two species of soil-living arthropods (springtails: Collembola) with direct development but assumed differ- ences in self-organizing behavior. We expected that the species with more pronounced social interactions (Hypogastrura tullbergi) should be less influenced by environmental factors and species interactions across all age classes, than Folsomia quadrioculata that is not known to exhibit social behavior. We used variance partitioning to examine the relative contributions of soil variables, vegetation composition, and other Collembola, vs. spatial variables (as a proxy for intraspecific interactions, i.e., self-organization), on the distribution of the two species and three of their age classes. We show that two coexisting species with clear aggregation patterns greatly differ in how much the environment contributes to affecting the species’ spatial structure. Local F. quadrioculata abundance was explained by different spatial and environmental variables depending on age class. In contrast, for H. tullbergi, spatial variables explained more of the abundance variation in all age classes. These differences have implications for the general predictability of changes in spatial structuring of species, as self-organized species may be less likely to respond to changes in environmental factors. Our results show that because age classes may be differentially affected by environmental conditions, caution should be taken when assuming that species traits can be applied to all developmental stages in a species. Key words: age classes; biological interaction; Collembola; environmental constrain; intraspecific interaction; Moran’s eigenvector map analysis; population ecology; self-organization; soil fauna; spatial configuration; variance partitioning. Received 2 October 2017; revised 20 November 2017; accepted 22 November 2017. Corresponding Editor: Uffe N. Nielsen. Copyright: © 2018 Widenfalk et al. This is an open access article under the terms of the Creative Commons Attribution License, which permits use, distribution and reproduction in any medium, provided the original work is properly cited. E-mail: [email protected] INTRODUCTION (Lima et al. 2009). To develop theories of com- munity organization, we need to describe pat- Relating the spatial structure of species and terns that can be compared across systems, and populations to environmental conditions is a first this needs to be done at all the scales that could step to understanding the factors underlying spe- influence the system (Levin 1992). Analyses of cies distributions and community composition spatial community distribution patterns com- (Cottenie 2005). This is important for manage- monly view all conspecifics as behaving similarly ment of both threatened species and pest species and as having the same traits (McGill et al. 2006) ❖ www.esajournals.org 1 January 2018 ❖ Volume 9(1) ❖ Article e02058 WIDENFALK ET AL. a practice that has been criticized by Violle et al. performing spatial analyses (Tilman and Kareiva (2012). Rudolf and Rasmussen (2013) added to 1997, Borcard et al. 2004, Griffith and Peres-Neto this criticism by emphasizing the risk of missing 2006, Beale et al. 2010). One of the most promis- important differences between life stages (i.e., ing to capture spatial patterns at a range of scales age classes) when traits are used at the species simultaneously are Moran’s eigenvector map level. This risk seems especially high in species (MEM) analyses (Borcard et al. 2004, 2011). Spa- where food or habitat requirements are dramati- tial variables can be interpreted as representing cally different between juveniles and adults, as in either dispersal constrains or biotic interactions many amphibians and most insects. However, causing distinct spatial distribution patterns not species that live in the same macro-habitat connected to environmental variables (Cottenie throughout their lives might also differ in their 2005). Fine-scale spatial patterns are more likely spatial distribution with age: For example, in to be connected to biotic interactions. These connection with reproduction, feeding prefer- fine-scalepatternsarepossibletocaptureby ences, drought or temperature tolerance, and MEM analyses, whereas larger scale descriptors strength of interspecific interactions may show such as trend surface analyses usually fail age-specific differences (Gilbert et al. 1999, (Borcard et al. 2004). Amarasekare and Sifuentes 2012). The Collembola (springtails) are excellent Most populations show spatial structuring study organisms to test whether the species level within their habitat (Tilman and Kareiva 1997). is a reliable unit for spatial distribution analyses. However, the degree of spatial structuring and its Their lower dispersal ability compared to, for causes vary greatly among species. Both biotic example, flying insects makes their immediate and abiotic factors, including environmental con- presence at a site much less stochastic. And with ditions, interactions with other species and direct development, with juveniles and repro- resources, may cause individuals to aggregate in ducing adult stages usually co-occurring in the specific areas (Wiens 1976). Species may also same habitat (Hopkin 1997), age dependency show “self-organized” spatial structuring (sensu will be more subtle and general, than the extreme Parrish and Edelstein-Keshet 1999), that is, a differences in organisms with metamorphosis behavior not driven by specific habitat or envi- and switching of resources between juveniles ronmental factors, but caused by internal factors and adults. However, in some Collembola spe- within a population, such as responses on odor cies, age classes show different preferences (pheromones), vocal or visual stimuli. Reasons regarding food quality (Jensen et al. 2006). This for aggregation, not directly related to environ- indicates that there may be age-related differ- mental variables, include reducing the risk for ences in behavior that can result in different predation (Hamilton 1971), increasing reproduc- distribution patterns even in this taxon, which tive success (Levitan and Young 1995), or can have effect on, for example, the function of improved ability to detect favorable patches (Lei- the species in the ecosystem (Sato and Watanabe naas et al. 2015), as well as other benefits of social 2014). In addition, dispersal might be more group living (Benoit et al. 2009, Vanthournout restricted in young individuals (Johnson and et al. 2016). The degree to which self-organized Wellington 1983), both as a function of smaller behavior influences the spatial distribution of size, but also due to a restricted ability to use all individuals depends on its relative dominance micro habitats because of a higher sensitivity to over sensitivity to environmental factors. In addi- drought (Leinaas and Fjellberg 1985, Hertzberg tion to these current conditions, present distribu- and Leinaas 1998). Since eggs are deposited in tion patterns may to varying degree also reflect batches, and often by aggregating adults past structuring processes owing to dispersal lim- (Hopkin 1997), reduced dispersal of smaller itation. Effects of these drivers on spatial distribu- stages may lead to age differences in aggregating tion will in many organisms be age dependent, tendency even without self-organization of the and comparison of juveniles vs. adults may juveniles. As collembolans have an important reveal important components of the dynamics. ecosystem functioning through their role in Space can be described in several different decomposition and nutrient cycling of soils ways, and there are a number of methods for (Petersen 1994), and different species and life ❖ www.esajournals.org 2 January 2018 ❖ Volume 9(1) ❖ Article e02058 WIDENFALK ET AL. stages may have different level of impact, it is (Hertzberg et al. 1994), while its drought sensi- important to understand underlying mecha- tivity may further affect its spatial distribution nisms for their spatial distribution to be able to (Hertzberg and Leinaas 1998). However, no dis- predict potential changes in functioning (Wardle tinct group coordination has been observed in 2006). this or any related species in the field, nor during The tendency to aggregate is diverse and extensive lab studies of the species (Sengupta widespread among collembolan taxa (Hopkin 2015). We therefore hypothesize that environ- 1997 and references therein), ranging from spe- mental constrains will be more important than cies where