Data from: Species interactions, environmental gradients and body size shape population niche width
Creators
- 1. University of Jyväskylä
- 2. Norwegian University of Science and Technology
- 3. Norwegian Institute for Nature Research
- 4. UiT The Arctic University of Norway*
Description
Competition for shared resources is commonly assumed to restrict population-level niche width of coexisting species. However, the identity and abundance of coexisting species, the prevailing environmental conditions, and the individual body size may shape the effects of interspecific interactions on species' niche width.
Here we study the effects of inter- and intraspecific interactions, lake area and altitude, and fish body size on the trophic niche width and resource use of a generalist predator, the littoral-dwelling large, sparsely-rakered morph of European whitefish (Coregonus lavaretus; hereafter LSR whitefish). We use stable isotope, diet and survey fishing data from 14 subarctic lakes along an environmental gradient in northern Norway.
The isotopic niche width of LSR whitefish showed a humped-shaped relationship with increasing relative abundance of sympatric competitors, suggesting widest population niche at intermediate intensity of interspecific interactions. The isotopic niche width of LSR whitefish tended to decrease with increasing altitude, suggesting reduced niche in colder, less productive lakes.
LSR whitefish typically shifted to a higher trophic position and increased reliance on littoral food resources with increasing body size, although between-lake differences in ontogenetic niche shifts were evident. In most lakes, LSR whitefish relied less on littoral food resources than coexisting fishes and the niche overlap between sympatric competitors was most evident among relatively large individuals (>250 mm). Individual niche variation was highest among >200 mm long LSR whitefish, which likely have escaped the predation window of sympatric predators.
We demonstrate that intermediate intensity of interspecific interactions may broaden species' niche width, whereas strong competition for limited resources and high predation risk may suppress niche width in less productive environments. Acknowledging potential humped-shaped relationships between population niche width and interspecific interactions can help us understand species' responses to environmental disturbance (e.g., climate change and species invasions) as well as the driving forces of niche specialization.
Notes
Data files
Lake_modelling_data.csv : lake-specific data used in linear models predicting isotopic niche width (TA and SEAc), trophic diversity (MNND) and among-individual diet variation (V) of LSR whitefish as a function of interspecific (Inter) and intraspecific (Intra) interactions and lake altitude and surface area.
Individual_SIA_data.txt : individual stable isotope data of LSR whitefish collected from the 14 study lakes.
Individual_SCA_data.txt : individual stomach contents (diet) data of LSR whitefish collected from the 14 study lakes.
All_fishes_SIA_data.txt : individual stable isotope data of the most abundant fish species collected from the 14 study lakes used to plot size-dependent niche shifts in LR (Figure 4) and TP (Figure 5) estimates.
Data in columns
"waterBody" = lake name
"waterBodyID" = unique lake number in Norwegian lake databases
"Altitude" = altitude aka elevation in meters above the sea level
"Area" = lake surface area in square kilometers (km2)
"MaximumDepth" = lake maximum depth in meters (m).
"Inter" = proxy for intensity of interspecific interactions measured as the proportion of fish species other than whitefish in the total multi-mesh survey gillnet catches (i.e., total fish biomass in grams including fish from all habitats) in each lake.
"Intra" = proxy for intensity of intraspecific resource competition. This proxy variable was standardized for different sampling efforts in each study lake (Table S1) by calculating total catch per unit of effort (CPUE; measured as the number of whitefish individuals caught per 100 m2 gillnet area per night), including all present whitefish morphs in each lake.
"TA" = total convex hull area (TA; see Jackson et al., 2011 for details) encompassing the LR and TP values of all LSR whitefish individuals in each lake used as a proxy for population (or "isotopic") niche width.
"SEAc" = sample-size corrected standard ellipse area (SEAc; Jackson et al., 2011) encompassing the core set of LR and TP values of LSR whitefish individuals in each lake, used as a proxy for population (or "isotopic") niche width.
"V" = the degree of among-individual diet variation (V = 1 – mean PSi). See below the description for proportional diet similarity index PSi.
"MNND" = mean nearest neighbour distance (MNND) based on Euclidean distances between individual data points in the LR – TP space and measuring trophic diversity among individuals (Jackson et al., 2011).
"scientificName" = Latin (scientific) name of the fish species
"Length" = total length of fish in millimeters (mm).
"PSi" = proportional diet similarity index calculated for each individual fish with stomach fullness exceeding 10%. PSi indices were further used to calcualte the degree of among-individual diet variation (V = 1 – mean PSi) in each whitefish population following the equations described in Bolnick et al. (2002) and Svanbäck et al. (2015). The PSi index compares each individual's diet to that of the entire population, with values ranging between 0 and 1. In populations where individuals specialize on different kinds of prey, the PSi values tend to be low and the resulting population-level V values tend to be high, i.e. approaching 1 (Bolnick et al., 2002; Svanbäck et al., 2015).
"d13C" = stable carbon isotope value (δ13C) of fish muscle tissue used in calculation of littoral reliance estimates (LR, see descriptions below).
"d15N" = stable nitrogen isotope value (δ15N) of fish muscle tissue used in calculation of trophic position estimates (TP, see description below).
"LR" = estimate of the relative reliance of fish on littoral (versus pelagic) carbon sources calcualted using the two-source isotopic mixing model described in Post (2002). See more detailed description of LR calculation below.
"TP" = estimate of the trophic position of fish in the lake food web calcualted using the two-source isotopic mixing model described in Post (2002). See more detailed description of TP calculation below.
The LR (eqn 1) and TP (eqn 2) estimates were calculated using the linear isotopic mixing models described in Post (2002):
LR = (δ13Cfish – δ13Cpel) / (δ13Clit – δ13Cpel) eqn (1)
TP = λ + (δ15Nfish – [δ15Nlit x LR + δ15Npel x (1 – LR)] / Δn eqn (2)
where δ13Cfish and δ15Nfish refer to isotope values of individual fish; δ13Clit, δ15Nlit, δ13Cpel and δ15Npel refer to the lake-specific δ13C and δ15N values for the littoral and pelagic isotopic end-members; λ is the trophic position of the organisms used to estimate δ15Nlit and δ15Npel, (here λ = 2 for primary consumers); and Δn is the mean trophic fractionation of muscle tissue δ15N (i.e., 2.9‰; McCutchan et al., 2003). For LR calculation, δ13Cfish were corrected for trophic fractionation by subtracting 1.3‰ from the original δ13C value (McCutchan et al., 2003). The littoral and pelagic isotopic end-members were defined as the mean isotope values of algae-grazing littoral benthic invertebrates (i.e., snails, Gammarus lacustris amphipods and chironomid larvae; δ13C ≥ -25‰) and pelagic zooplankton (δ13C ≤ -28‰), respectively.
References
Bolnick, D.I., Yang, L.H., Fordyce, J.A., Davis, J.M., & Svanbäck, R. (2002). Measuring individual-level resource specialization. Ecology, 83, 2936–2941. https://doi.org/10.1890/0012-9658(2002)083[2936:MILRS]2.0.CO;2
Jackson, A.L., Inger, R., Parnell, A.C., & Bearhop, S. (2011). Comparing isotopic niche widths among and within communities: SIBER – Stable Isotope Bayesian Ellipses in R. Journal of Animal Ecology, 80, 595–602. https://doi.org/10.1111/j.1365-2656.2011.01806.x
McCutchan, J.H., Jr, Lewis, W.M., Jr, Kendall, C., & McGrath, C.C. (2003). Variation in trophic shift for stable isotope ratios of carbon, nitrogen, and sulfur. Oikos, 102, 378–390. https://doi.org/10.1034/j.1600-0706.2003.12098.x
Post, D.M. (2002). Using stable isotopes to estimate trophic position: models, methods, and assumptions. Ecology, 83, 703–718. https://doi.org/10.1890/0012-9658(2002)083[0703:USITET]2.0.CO;2
Svanbäck, R., & Persson, L. (2004). Individual diet specialization, niche width and population dynamics: implications for trophic polymorphism. Journal of Animal Ecology, 73, 973–982. https://doi.org/10.1111/j.0021-8790.2004.00868.x
Funding provided by: Academy of Finland
Crossref Funder Registry ID: http://dx.doi.org/10.13039/501100002341
Award Number: 340901
Funding provided by: Academy of Finland
Crossref Funder Registry ID: http://dx.doi.org/10.13039/501100002341
Award Number: 317495
Funding provided by: Norges Forskningsråd
Crossref Funder Registry ID: http://dx.doi.org/10.13039/501100005416
Award Number: 186320
Funding provided by: Norges Forskningsråd
Crossref Funder Registry ID: http://dx.doi.org/10.13039/501100005416
Award Number: 243910