10.5061/DRYAD.XPNVX0KBF
Parain, Elodie C.
University of Fribourg
Gray, Sarah M.
0000-0002-4025-6487
University of Fribourg
Bersier, Louis-Félix
0000-0001-9552-8032
University of Fribourg
The effects of temperature and dispersal on species diversity in natural
microbial metacommunities
Dryad
dataset
2019
Diversity-dispersal relationship
Protists
Sarracenia purpurea
Climate-change ecology
Swiss National Science Foundation
31003A_138489
Swiss National Science Foundation
https://ror.org/00yjd3n13
Grant 31003A_138489
2020-01-06T00:00:00Z
2020-01-06T00:00:00Z
en
https://doi.org/10.1038/s41598-019-54866-9
74148 bytes
3
CC0 1.0 Universal (CC0 1.0) Public Domain Dedication
Dispersal is key for maintaining biodiversity at local- and regional
scales in metacommunities. However, little is known about the combined
effects of dispersal and climate change on biodiversity. Theory predicts
that alpha-diversity is maximized at intermediate dispersal rates,
resulting in a hump-shaped diversity-dispersal relationship. This
relationship is predicted to flatten when competition increases. We
anticipate that this same flattening will occur with increased temperature
because, in the rising part of the temperature performance curve,
interspecific competition is predicted to increase. We explored this
question using aquatic communities of Sarracenia purpurea from early- and
late-successional stages, in which we simulated four levels of dispersal
and four temperature scenarios. With increased dispersal, the hump shape
was observed consistently in late successional communities, but only in
higher temperature treatments in early succession. Increased temperature
did not flatten the hump-shape relationship, but decreased the level of
alpha- and gamma-diversity. Interestingly, higher temperatures negatively
impacted small-bodied species. These metacommunity-level extinctions
likely relaxed interspecific competition, which could explain the absence
of flattening of the diversity-dispersal relationship. Our findings
suggest that climate change will cause extinctions both at local- and
global- scales and emphasize the importance of intermediate levels of
dispersal as an insurance for local diversity.
We sampled S. purpurea inquiline communities from the site ‘Champ Buet’ in
Switzerland, which is situated at 500 m above sea level (CB, 46°36’50’’N,
6°34’50’’E). Eighty leaves that were nearly open were marked at the
beginning of June 2014, and 80 additional nearly opened leaves were marked
two weeks later. Thus, the inquiline communities within the leaves were
allowed to develop for four weeks (‘late-succession’) and two weeks
(‘early-succession’), respectively. All 160 leaves were sampled at the
same time. The sampled water from each successional stage was place into
two separate sterilized 1L Nalgene bottles. The bottles were brought back
to the laboratory and chilled at 4°C to temporarily slow community
dynamics until the set-up of the experiment the following day. The overall
density of the protists was measured for the pooled early- and pooled
late- succession communities. The following procedure was then applied to
both stages. The water was diluted in order to reach a density of 10’000
individuals of protists per mL and eighty 50 mL macrocentrifuge tubes were
filled with a 10 mL aliquot of these dilutions. As a basal food resource,
we added 500 µL of an autoclaved Tetramin fish food solution
(concentration of 2 mg of solid fish food in 1 mL of DI water) into each
tube. This resource is consumed by the bacteria in the system, which are
then consumed by the protists and rotifers. The 4 x 4 x 2 factorial design
included four dispersal levels (No-, Low-, Medium-, and High-dispersal)
and four temperature treatments (Local, -2.5°C below the local average
temperature, +2.5°C and +5°C above the local average temperature) and two
levels of community succession (Early succession and Late succession). Our
temperature treatments were based on the natural June temperatures of the
field site (minimum: 10°C, average: 15.5°C, maximum: 20.9°C) according to
30 years of data acquired by WorldClim (www.worldclim.org, accessed
January 2017). Each treatment was composed of five tubes forming a
metacommunity, totaling 160 tubes, which were placed in Panasonic MIR-154
incubators for the experiment, equipped with new lightbulbs and with light
and temperature data loggers to exclude possible unwanted variability in
our experiment; all tubes were placed in a randomized design within each
incubator and this design was changed after every dispersal event.
Dispersal was manipulated twice a week by transferring different numbers
of individuals between the tubes of a treatment. These dispersal events
were done separately for every treatment: the individuals of a treatment
were only allowed to disperse within their specific metacommunity. Within
each treatment, an aliquot of 100 µl was removed from each of the five
tubes and combined into a 15 mL sterile macrocentrifuge tube. This mixture
was then diluted with autoclaved DI water according to the dispersal level
of that treatment. This dilution was necessary to maintain the same volume
of water across all treatments, while allowing different numbers of
individuals to disperse according to treatment. For the ‘high dispersal’
treatment, 100 µL of this mixture was returned into each of the 5 tubes
without dilution. For the ‘medium dispersal’ treatment, the mixture was
diluted ten times and added to each of the 5 tubes, and 100 times for the
‘low dispersal’ treatment. For the no-dispersal treatment, 100 µl aliquots
were also removed and re-pipetted into the same tube. The experiment
lasted for 7 weeks, after an initial incubation of 8 days in the “Local
Temperature” incubator. Communities were fed once a week with 500 µL of
fish food at the same concentration as described above. Every week, we
sampled 100 µL of water in each tube after gently mixing, and estimated
the density and composition of protist- and rotifer- species. Individuals
were identified according to their morphology and categorized into 18
morphospecies. We used an inverted microscope at 100x magnification and a
Thoma cell microscope plate to count the protists and rotifers. Densities
of common species were estimated on two grids of the Thoma cell (number of
individuals per 0.2 µL). Densities of rare species (observed only outside
of the Thoma grid) were set to 0.1.