List of materials in supporting information
Appendix 1. Description of artificial channel “mesocosm” structure used in
experiments and methods used to measure guppy excretion
Appendix 2. Details of the experiments combined to generate the dataset used in
this paper.
Figure S1. A comparison of N excretion (a) and P excretion (b) between the two
experiments.
Table S1. Characteristics of streams used for guppy-mediated nutrient recycling
study.
Table S2. Results of model selection procedure for N excretion based on
experimental data.
Table S3. Results of model selection procedure for N excretion from natural streams.
Table S4. Results of model selection procedure for P excretion based on
experimental data.
Table S5. Results of model selection procedure for P excretion from natural streams.
Appendix 1. Description of artificial channel “mesocosm” structure used in
experiments and methods used to measure guppy excretion: In our paper we combine
data from previously published experiments to make a prediction about how the
individual, population and environmental correlates of guppy life history evolution
influence nutrient recycling. All of these experiments have used exactly the same
artificial experimental channels; here we provide a brief description of the
experimental set up, which was described in detail in manuscripts based on these
experiments (Bassar et al., 2010; El-Sabaawi et al., In review). Eight flow-through
cinder block channels were built adjacent to Ramdeen Stream, a tributary of the
Arima River (Trinidad), and were laterally divided into 16 experimental units
(mesocosms, 3.0 x 0.5 m). Water was diverted to the mesocosms from a nearby
fishless spring via a settling tank, and then delivered to each mesocosm using
garden hoses (100 ft long, 3/4 inches wide). Discharge was maintained between 75
L hr-1 and 140 L hr-1 depending on natural spring flow rates, which can vary
between seasons and years due to differences in hydrological conditions (e.g. wet
season vs. dry season, El-Nino or La-Nina years vs. average years). Water depth was
maintained at ~15 cm in each channel. The bottom of each mesocosm was prepared
using a commercially available gravel and sand mix that was rinsed to remove silt.
An equal mixture of rinsed sand and gravel was evenly spread to a depth of 5 cm at
the bottom of each mesocosm. Mesocosms were then conditioned in running water
between 7 and 14 days to allow for the build up of biofilm and benthic organic
matter. Invertebrates and benthic organic matter were collected using kick nets
from the slow-running portions of a nearby tributary of the Arima River. The
collection area was equivalent to total mesocosm area. Large larvae of predaceous
insects (such as odonates) were removed by hand, and the remaining material was
homogenized then distributed equally between all mesocosms. Insects were allowed
one week to colonize the mesocosms before each experiment began. In each
experiments guppies were collected from natural HP and LP populations, which
were then marked using elastomer and introduced into the channels. Each
experiment ran for ~28 days, which is enough for the guppies to go through a single
reproductive cycle. Similar ecosystem response variables (algal accrual, leaf litter
decomposition, invertebrate standing stocks and density) were measured in each
experiment using the same methods. Light levels, which were monitored throughout
the experiments using HoBo® light loggers and periodic PAR measurements, were
controlled by agricultural mesh. In both studies, initial body size distribution and
male:female ratios were the same (1:1). The Bassar/density experiments measured
the effects of guppy phenotype on ecosystem function in two guppy density
treatments. Light levels were kept low (in line with LP sites), but total guppy density
was either 24 or 12 guppies per channel, which is representative of guppy densities
in LP and HP sites respectively. In the El-Sabaawi/light experiment, density was
kept low (12 guppies per channel), but light was varied to reflect light differences in
HP and LP sites. The Bassar experiment was executed twice using two different
populations (Aripo and Guanapo), but the ElSabaawi experiment only used guppies
from the Aripo River. In the paper we only use data from the Aripo experiments.
In all experiments and field studies guppy excretion was measured by
catching 3-4 guppies from each experimental channel using dipnets, and then
placing the guppies in individual ~1 L bags of filtered spring water, which were
maintained at ambient water temperature. Ammonium N hr-1 and soluble reactive
phosphorous P hr-1 were measured before guppies were introduced in the bag, and
and after 20 minutes of incubation. Handling time was estimated prior to the
experiments, and excretion trials were constructed to minimize handling stress
(Whiles et al., 2009). Ammonium was measured using the fluorometric method
(Holmes et al., 1999; Taylor et al., 2007), while phosphorus was measured using the
colormetric molybdate method (Parsons, Maita & Lalli, 1984). Each guppy was
weighed and measured (standard length). In all experiments guppy excretion was
measured on day 27.
Literature Cited
Bassar R.D., Marshall M.C., Lopez-Sepulcre A., Zandona E., Auer S.K., Travis J., et al.
(2010) Local adaptation in Trinidadian guppies alters ecosystem processes.
Proceedings of the National Academy of Sciences of the United States of
America, 107, 3616-3621.
El-Sabaawi R.W., Bassar R.D., Rakowski C., Marshall M.C., Bryan B.L., Thomas S.A., et
al. (In review) Intraspecific phenotypic differences in fish affect ecosystem
processes as much as bottom-up factors Oikos.
Holmes R.M., Aminot A., Kerouel R., Hooker B.A. & Peterson B.J. (1999) A simple and
precise method for measuring ammonium in marine and freshwater
ecosystems. Canadian Journal of Fisheries and Aquatic Sciences, 56, 18011808.
Parsons T.R., Maita Y. & Lalli C.M. (1984) A manual of chemical and biological
methods for seawater analysis, Pergamon Press, Oxford Oxfordshire ; New
York.
Taylor B.W., Keep C.F., Hall R.O., Koch B.J., Tronstad L.M., Flecker A.S., et al. (2007)
Improving the fluorometric ammonium method: matrix effects, background
fluorescence, and standard additions. Journal of the North American
Benthological Society, 26, 167-177.
Whiles M.R., Huryn A.D., Taylor B.W. & Reeve J.D. (2009) Influence of handling stress
and fasting on estimates of ammonium excretion by tadpoles and fish:
recommendations for designing excretion experiments. Limnology and
Oceanography: Methods, 7, 1-7.
Appendix 2. Details of the experiments combined to generate the dataset used in this paper. Low density means = 12 female
guppies per channel, which reflects density in HP sites, and high density = 24 guppies per channel, which reflects density in LP
sites. High light = ~68 x 106 and low light = ~16 x 106 lumen ft-1day-1, reflecting values found in HP and LP sites respectively. River
is the origin of wild caught guppies used in the experiment. ARP is the Aripo River. Replicates is the number of channels
representing each treatment (out of 16 total artificial channels). N is the number of female or juvenile guppies sampled for
excretion.
Figure S1. A comparison of N excretion (a) and P excretion (b) between the two
experiments. The data are from a single treatment, which was identical in both
experiments: the low density treatment in Bassar et al. (2010), which was also
conducted at low light, and the low light treatment in El-Sabaawi et al. (in review),
which was conducted at low density. Light level and guppy density were equal in
both experiments.
The light experiment (El-Sabaawi et al.) had slightly bigger guppies on average than
the density experiment (Bassar et al. 2010), and therefore slightly higher individual
excretion rates. There were more pronounced but relatively small differences in P
excretion between the experiments in individual excretion rate, as well as the
relationship between excretion rate and body size. Phosphorus excretion was
slightly higher and more strongly related to body size in guppies from the ElSabaawi/light experiment compared to guppies from the Bassar/density
experiment.
Log N excretion
(ug N per fish per hour)
2.0
A
Bassar
El-Sabaawi
1.5
Variable
Body size
Experiment
Experimentx body size
1.0
0.5
0.0
-4
-3
-2
-1
F ratio (P value)
45.21 (<0.001)
4.6 (0.04)
0.03 (0.85)
0
Log Body size (wet mass,g)
Log P excretion
(ug P per fish per hour)
1.5
Bassar
El-Sabaawi
B
1.0
Variable
Body size
Experiment
Experimentx body size
0.5
0.0
-4
-3
-2
-1
Log Body size (wet mass,g)
0
F ratio (P value)
14.4(<0.001)
46.47(<0.001)
10.93(0.002)
Table S1. Characteristics of streams used for guppy-mediated nutrient recycling study. Data are from pools only, which are
assumed to be the primary guppy habitat in stream systems. For methods please see El-Sabaawi et al. (2012). Density is the
number of guppies per area, measured using depletion curves (CPUE; Catch per Unit Effort). See manuscript for
methodological details.
Stream
Predation
Slope
Light availability
(% open canopy)
Arima
Aripo
Guanapo
Marianne
HP
LP
HP
LP
HP
LP
HP
LP
South
South
South
South
South
South
North
North
23.4(12.6)
4.4(2.0)
23.6(10.0)
8.3(2.0)
4.9(8.3)
18.1(13.1)
21.1(14.9)
12.3(6.2)
Density
(m-2)
Discharge
L.S-1
1.01
3.06
0.27
19.4
2.02
5.02
5.37
N/A
32.
15.8
52.7
41.1
32.6
1323
1478
SRP
(g P.L1
)
82
24.3
34.5
7.7
37.4
44.7
14.6
6.1
Ammonium
(g N.L-1)
2.4
0.6
5.8
3.3
3.8
2.8
2.9
1.9
Table S2. Results of model selection procedure for N excretion based on experimental data. Body size is body size lntransformed wet mass (g). D.F. is degrees of freedom. L.L. in the log likelihood ratio. AICc is the corrected Akaike Information
Criterion, and ∆AICc is the difference in AIC between model and most parsimonious model. Only models with ∆AICc < 4 are
reported.
Table S3. Results of model selection procedure for N excretion from natural streams. Body size is body size ln-transformed wet
mass (g). D.F. is degrees of freedom. L.L. in the log likelihood ratio. AICc is the corrected Akaike Information Criterion, and
∆AICc is the difference in AIC between model and most parsimonious model. Only models with ∆AICc < 4 are reported
Table S4. Results of model selection procedure for P excretion based on experimental data. Body size is body size lntransformed wet mass (g). D.F. is degrees of freedom. L.L. in the log likelihood ratio. AICc is the corrected Akaike Information
Criterion, and ∆AICc is the difference in AIC between model and most parsimonious model. Only models with ∆AICc < 4 are
reported
Table S5. Results of model selection procedure for P excretion from natural streams. Body size is body size ln-transformed wet
mass (g). D.F. is degrees of freedom. L.L. in the log likelihood ratio. AICc is the corrected Akaike Information Criterion, and
∆AICc is the difference in AIC between model and most parsimonious model. Only models with ∆AICc < 4 are reported