Jurnal Kece Plankton!
Jurnal Kece Plankton!
Jurnal Kece Plankton!
Abstract
We used an observed abrupt shift in the dominance pattern of two coexisting copepod species in Muggelsee, a
shallow eutrophic lake in Germany, to investigate mechanisms leading to this shift, by embedding our findings
into the framework of intraguild predation theory and theoretical scenarios of threshold-driven regime shifts. We
proposed that the abrupt increase in Cyclops kolensis, changing its status from a rare to the dominant species as
available algal prey declined in the lake, was due to its superior exploitative competition for commonly consumed
algal prey. However, C. kolensis was only able to thrive in the emerging low food niche when abundances of
competing larger Cyclops vicinus, a predator of C. kolensis juveniles, fell below a critical threshold. This is
consistent with the state threshold scenario of regime shift theory, for which a response variable exhibits an
abrupt shift, here C. kolensis, after the driver (C. vicinus) crosses a threshold. We confirmed the nonlinear
relationship between the two copepod species by excluding potentially matching abrupt changes in other abiotic
and biotic driving variables, and successfully classifying C. kolensis abundance probability on the basis of C.
vicinus abundances using logistic generalized linear modeling. C. vicinus decline followed the driver threshold
scenario of regime shift theory, whereby an abrupt change in a driver (cryptophytes) causes a sudden shift in a
response variable (C. vicinus). We illustrated how observational data on plankton communities match predictions
derived from ecological theory.
In freshwater ecosystems, relative community composition of zooplankton ensembles constantly fluctuates over
the years. This is because the communities are embedded in
a highly dynamic and complex system governed by a huge
range of extrinsic and intrinsic forces, where the latter often
mediate the effects of the former (Sommer et al. 2012).
Thus, changing conditions can favor different species,
depending on their ecological niches. The resulting changes
in abundance can thereby be gradual or abrupt with
elapsing time. Abrupt changes constitute regime shifts and
may be the result of different mechanisms. The regime shift
might arise from an equally sudden change in a driving
variable, or it may be a drastic answer to a gradual
changing driving variable surpassing a threshold. Thereby
the drastic response may or may not be the result of a jump
between alternative stable states (Andersen et al. 2009;
Scheffer 2009; Bestelmeyer et al. 2011). In recent years,
drastic responses in ecosystem dynamics have gained
increasing attention in ecology because of their seeming
unpredictability and potentially large effect on an ecosystem. Hence, if a regime shift occurs, it is desirable to first
differentiate whether potential drivers exhibit matching
sudden changes or if their change is gradual. If the latter is
the case, important insight into ecological systems can be
gained by quantifying potential thresholds in those drivers.
Extrinsic changes driven by climate and trophic states,
which many freshwater systems have been subjected to over
the past decades (Mooij et al. 2005; Adrian et al. 2009),
have a large effect either at the single species level
(Gyllstrom et al. 2005; Seebens et al. 2008) or on plankton
communities as a whole (Adrian et al. 2006; Elliot and May
2008; Wagner and Adrian 2009). General concepts
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Methods
Study siteThe Muggelsee classifies as a shallow,
polymictic, and eutrophic lake, situated in the temperate
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Results
Copepod long-term trends and phenologyThe cyclopoid
copepod winter community in the Muggelsee was dominated by C. kolensis and C. vicinus. Comparing the results
from trend and regression tree analyses revealed that
whereas C. vicinus abruptly decreased in abundance in 1988
and 1993, its overall dynamics were dominated by a
significant gradual decline over the entire study period
(Figs. 2a, 3a; Table 1). By contrast, C. kolensis underwent
one abrupt abundance increase in 1995 (Figs. 2a, 3b).
Between 1980 and 1995before this abrupt changeC.
kolensis comprised, on average, 2.5% (0%, 12%, and 2% in
autumn, winter, and spring, respectively) of the cyclopoid
copepod winter community, and became by far the most
dominant species in 1995 to 2010 (6%, 86%, and 57% in
autumn, winter, and spring, respectively; Fig. 2a).
C. kolensis developed its pelagic population between
September and May (Fig. 2c). The phenology of C. kolensis
remained unchanged over the entire investigation period. C.
vicinus was usually present throughout the year, with
population peaks in spring and autumn. A 1 month phenology
shift toward later in autumn was observed for C. vicinus in the
second investigation period (1995 to 2010; Fig. 2b).
Trends in prey availability and water temperatureTotal
algal and cryptophyte biomass declined abruptly in 1991
and 1993, dropping by 46% and 31%, respectively, from the
5 yr period before the abrupt change to the following one
(Fig. 3d,e). Rotifers exhibited an abrupt decline in 1993,
where they lost 40% in mean abundance (5 yr comparison
as above), but increased again in 2002 (Fig. 3f). Rotifer
abundances never decreased below 245 individuals (ind.)
L21 during the entire study period (Fig. 4e,f). In addition
to the abrupt changes, significant monotonic trends for
water temperature, as well as cryptophyte and total algal
biomass, were found. Water temperature, with an average
rise of 0.9uC over the entire study period, was the only
variable with an increasing trend (Fig. 3c; Table 1).
Abiotic and biotic driversFollowing the Spearman
correlation coefficient, we found a significant relation
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Fig. 2. Copepod long-term trends and phenology. (a) September to May mean abundances of Cyclops kolensis (open circles) and
Cyclops vicinus (closed circles). (b) Phenology of C. vicinus and (c) C. kolensis, depicted as monthly mean abundances for the periods 1980
to 1994 (open circles) and 1995 to 2010 (closed circles). Mean abundances for each period were standardized with the maximal abundance
of the respective species and period.
0.03
20.05
20.09
20.02
20.09
0.05
CI
20.01
20.09
20.12
20.05
20.12
0.01
to
to
to
to
to
to
p value
0.06
20.03
20.06
0.02
20.06
0.09
0.04
0.03
0.00
0.46
0.00
0.16
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Fig. 3. Trends in prey availability and water temperature. Abrupt and linear trend dynamics in yearly means. Solid lines depict
robust regression models combining the largest abrupt changes in the mean from regression tree analysis for each variable, together with
significant trends from monotonic trend analysis if these exist for the respective variable. (a) Cyclops vicinus, (d) total algal biomass, and
(e) cryptophyte biomass were dominated by both abrupt changes and gradual linear trends in the mean. (b) Cyclops kolensis and (f)
rotifers were purely break-point driven, whereas (c) water temperature was solely marked by a linear trend. Data were standardized with
the maximum value of the respective variables.
Discussion
Abrupt changes in ecosystem responses to climate and
environmental change can have potentially large effects on
ecosystem functioning. However, the detailed nature of
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Fig. 4. Food niche separation for high abundance probability of Cyclops kolensis. C. kolensis (open circles) and Cyclops vicinus
(closed circles) abundance for the periods before 1980 to 1994 (left), and after 1995 to 2010 (right) the shift in C. kolensis abundance with
respect to (a, b) total algal biomass, (c, d) cryptophytes, and (e, f) rotifers. Dashed lines depict the thresholds estimated by the
classification summarized in Table 3.
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Table 2. Monotonic relationships between Cyclops kolensis or Cyclops vicinus and abiotic and biotic key drivers. The analysis was
based on Spearmans rank correlation coefficient. Spearmanss rho is given first, followed by the respective p-value in brackets. The
coefficients for C. kolensis were based on data ranging from 1995 to 2010, whereas those for C. vicinus were based on data from 1980 to 2010.
Water temperature
Total algal biomass
Cryptophytes
Rotifers
C. vicinus
C. kolensis*
C. kolensis**
C. vicinus*
C. vicinus**
C. vicinus***
0.16(0.54)
20.14(0.62)
20.23(0.39)
20.36(0.17)
0.50(0.05)
0.32(0.22)
20.18(0.51)
0.06(0.84)
20.63(0.01)
0.34(0.20)
20.4(0.02)
0.63(0)
0.72(0)
0.1(0.6)
20.26(0.16)
0.16(0.39)
0.13(0.5)
20.04(0.83)
20.19(0.32)
0.05(0.77)
0.26(0.17)
0.1(0.61)
* Results from trend-affected data; ** results from nonlinear detrended data; *** results from April to May means of nonlinear detrended data.
Water temperature
Total algal biomass
Cryptophytes
Rotifers
Threshold
AUC
7.02uC
6.15 mg L21
0.57 mg L21
419.91 ind. L21
0.67
0.95
0.94
0.65
CI
0.46
0.88
0.86
0.44
to
to
to
to
0.88
1.02
1.03
0.85
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Fig. 6. Driver threshold and state threshold regime shift scenarios. Analyses on the basis of fig. 1 in Andersen et al. 2009. (a, b, c)
The driver threshold scenario refers to the existence of a threshold in the driver (cryptophytes), which is linearly mediated to a response
(Cyclops vicinus). (a) The regime shift in cryptophyte biomass in 1993 was immediately followed by (b) a regime shift in C. vicinus
abundances, resulting in (c) a linear driver (cryptophytes) response (C. vicinus) scatter plot. The solid lines in driver and response variables
(panels a and b) stress the break-point components in the dynamics of the two variables. (d, e, f) The state threshold scenario refers to the
existence of a threshold in the response (Cyclops kolensis), but not in the driver (C. vicinus). (e) C. kolensis abundances underwent a regime
shift (d) after C. vicinus crossed a threshold, such that an abrupt change appears in the time series of C. kolensis and (f) a threshold appears in
the scatter plot between the two variables. The line in panel d solely depicts the linear trend component of C. vicinus abundance, since only
this part of the dynamics is relevant in this regime shift scenario.
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