Vol. 630: 1–12, 2019 MARINE ECOLOGY PROGRESS SERIES Published November 7 https://doi.org/10.3354/meps13154 Mar Ecol Prog Ser OPENPEN FEATURE ARTICLE ACCESSCCESS Implications of using different metrics for niche analysis in ecological communities Adam Gouraguine1,*, Carlos J. Melián2, Olga Reñones3, Hilmar Hinz4, Heather Baxter5, Luis Cardona6, Joan Moranta3 1School of Biological Sciences, University of Essex, Colchester CO4 3SQ, UK 2Department of Fish Ecology and Evolution, Center for Ecology, Evolution and Biogeochemistry, Swiss Federal Institute of Aquatic Science and Technology, 6047 Kastanienbaum, Switzerland 3Instituto Español de Oceanografía (IEO), Centre Oceanogràfic de les Balears, Ecosystem Oceanography Group (GRECO), Moll de Ponent sn, 07015 Palma, Spain 4Department of Ecology and Marine Resources, Instituto Mediterráneo de Estudios Avanzados IMEDEA (CSIC-UIB), 07190 Esporles, Spain 5School of Geographical and Earth Sciences, University of Glasgow, Glasgow G12 8QQ, UK 6IRBio and Department of Evolutionary Biology, Ecology and Environmental Science, Faculty of Biology, University of Barcelona, 08007 Barcelona, Spain ABSTRACT: Explaining the mechanisms driving niche partitioning among species is of great impor- tance in ecology. Unlike the fundamental niche, a species’ realised niche can only be measured in situ, as a result of biotic and abiotic interactions defining its size. Following current methodology, the realised niche of a species is often influenced by the rare and divergent individuals of the community sampled. In this study, using fish on coral and temperate reefs as an example, behavioural empirical data were col- lected to estimate realised niche sizes and niche overlaps. Niche measurements were made using the total area of the convex hull (TA), but as an alterna- tive, a metric not as strongly influenced by sample size, standard ellipse area (SEA), was also used. A comprehensive description is given, and context- Two fish species from the temperate reef community stud- dependent pros and cons of using both metrics are ied, East Atlantic peacock wrasse Symphodus tinca (fore - discussed. Additionally, an alternative sample size ground) and common two-banded seabream Diplodus vul- correction was presented for both metrics. The analy- garis (background). ses re vealed large differences in the sizes of realised Photo: Adam Gouraguine niches and their overlaps between species depend- ing on the measurement metric used. Regardless of the species, niche size and overlap were always KEY WORDS: Realised niche · Niche variability · larger for TA than SEA. Increasing sample size re - Standard ellipse area · Total area of the convex hull · duced niche size variability for both TA and SEA, but Algal reefs · Coral reefs · Teleostei the variation was always smaller for SEA than TA. We successfully adapted the SEA metric for analysis of behavioural niche components and demonstrated that measuring niche sizes using the 2 metrics, each 1. INTRODUCTION with their own strengths and weaknesses, can pro- duce contradictory results, the ecological conse- A species’ niche can be described as an n-dimen- quences of which are likely to be important. sional hyperspace, partitioned into environmental and trophic (resource) components representing the © The authors 2019. Open Access under Creative Commons by *Corresponding author: [email protected] Attribution Licence. Use, distribution and reproduction are un - restricted. Authors and original publication must be credited. Publisher: Inter-Research · www.int-res.com 2 Mar Ecol Prog Ser 630: 1–12, 2019 ecosystem (Hutchinson 1957). The fundamental niche In this study, using continuously recorded behav- is defined as the space a species occupies resulting ioural data, estimates were made of RN sizes and niche from the combination of physiological and behav- overlaps between the TA and SEA metrics for several ioural characteristics in the absence of intra- and abundant fish species with different life histories oc - inter-specific competition, when a species potentially curring in 2 distinct systems. Continuous observation occupies the space along all the axes of the ecosys- allows for identification of behaviours of interest and tem (Connell 1961, Begon et al. 2006). The presence associated habitats, followed by quantification and of dominant competitors and predation pressure comparison of behaviour expression and habitat use. along the ecosystem axes prevents the species from Consequently, multiple functional traits, rather than fully exploiting the entire ecosystem, so the con- a single trait (e.g. diet), can be considered to deter- strained space actually occupied by the species under mine species’ niches and their overlaps (Bellwood et these effects represents the realised niche (hereafter, al. 2004, Adam et al. 2015a). Using multiple func- RN) (Hutchinson 1957, Whittaker et al. 1973, Devic- tional traits allows for better estimates of comple- tor et al. 2010). To measure any dimension of the RN, mentarity and redundancy between species, as it is an interaction of the specific acting agents must be possible that species that appear to be functionally considered. Accordingly, RNs can only be assessed redundant based on a single trait can exhibit differ- using data collected in situ, where restricting agents ent levels of complementarity or redundancy when are operating. Unfortunately, there is a notable lack multiple functional traits are considered (Cadotte et of empirical studies encompassing field measure- al. 2011, Adam et al. 2015b). Further, use of abundant ments to determine species’ RNs across communities and life-history-diverse species aids in better repre- (Hooper et al. 2005, Tingley et al. 2014). sentation of the assemblage (numerically and behav- Furthermore, despite the existence of several simi- iourally), while sampling distinct systems allows for lar metrics, one of the common problems in the analy- subsequent observation of common patterns across sis of a RN is the calculation of its volume and amount systems. Accordingly, niche overlaps were compared of overlap between different species. Currently, RN by measuring the TA of each species, but as an alter- is most commonly calculated as the total area of the native, a metric based on SEA was also used. An convex hull (TA), where measurements tend to be attempt was made to give a comprehensive compari- char acterised by the individuals with the most ex - son of measurement-method-dependent differences treme positions within the sample (Jackson et al. in RN sizes, highlighting the importance of previ- 2011). The niche sizes obtained using this method ously unknown properties of different metrics for RN are generally influenced by a small number of diver- measurements, and demonstrating how past and gent individuals within the population, and thus meas- future findings could be altered. To address the issue uring the TA takes into consideration intraspecific var- of adequate sample sizes commonly encountered in iability. More recently, a different metric based on the ecological studies, an alternative sample size correc- measurement of the standard ellipse area (SEA) has tion was presented for both metrics, the pros and been proposed. To date, the SEA metric has only cons of both were discussed and recommendations been discussed for calculations of isotopic niche over- for their future use in ecological studies were made. laps (Jackson et al. 2011, Syväranta et al. 2013) but it could also be used for analysis of other components of the niche, to provide ecologically relevant infor- 2. MATERIALS AND METHODS mation about the individual, population or commu- nity (Bearhop et al. 2004). The use of SEA has been Field-based observations were conducted to meas- proposed mainly because it is not as strongly influ- ure RNs and their overlaps for several fish species on enced by sample size as the TA method. The SEA tropical coral- and temperate algal-dominated rocky represents the mean niche values of the community reefs. in question (Jackson et al. 2011). This method does not emphasise the importance of within-species indi- vidual variability and likely represents the niche 2.1. Sampling habitats and fish behaviours space delimited by the most frequent traits character- ising the individuals sampled. As such, the SEA niche Sampling took place on the coral reefs around measurement method represents the niche of the Curieuse Island of the Seychelles in the Indian Ocean majority of the individuals within the population, but and on the algal-covered rocky reefs off the western not the divergent individuals. coast of Mallorca Island in the Mediterranean Sea, in Gouraguine et al.: Niche analysis using different metrics 3 April and June of 2015, respectively (Fig. 1). In both ble and sand for the Seychelles and Posidonia ocean- locations, 8 different sites were sampled, each sepa- ica, erect, filamentous and turf algae, rock, rubble rated by a minimum distance of 500 m. and sand for Mallorca. On the coral reefs, data collection was conducted Based on the data from the visual censuses, the most between 1 and 12.5 m depth, while on the algal- abundant families were subsequently identified. To re - covered rocky reefs the sampling depth was between present a large (numerical abundance) and a diverse 1 and 15 m. At each site the fish community and habi- part of the assemblage (varied resource and habitat tat composition were initially assessed by underwa- use), the most commonly occurring species within the ter visual census (Harmelin-Vivien