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First evidence for long-term stasis in wet-tropics land snail community composition

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  • Pre-Construct Archaeology

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While spatial turnover in species composition is well documented (Whittaker 1975; Condit et al. 2002) much less investigation has been conducted over long‐time periods. Land snails provide a unique window to observe such patterns because their fossil shells not only allow for species‐level identifications and quantification of abundance (Schilthuizen 2011), but can also provide accurate radioisotope dates (Pigati et al. 2010). Here we compare species turnover and accumulation patterns in comparable temperate (Slovakia and the Czech Republic) and tropical (Malaysian Borneo) land snail datasets. These analyses show that while temperate communities demonstrated significant compositional change over the modern to Late Glacial Maximum (LGM) transition, tropical communities did not. This article is protected by copyright. All rights reserved.
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ECOGRAPHY
Ecography
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© 2018 e Authors. Ecography © 2018 Nordic Society Oikos
Subject Editor:
Jens-Christian Svenning
Editor-in-Chief: Miguel Araújo
Accepted 4 October 2018
00: 1–3, 2018
doi: 10.1111/ecog.03996
doi: 10.1111/ecog.03996 00 1–3
While spatial turnover in species composition is well documented (Whittaker 1975,
Condit et al. 2002) much less investigation has been conducted over long-time peri-
ods. Land snails provide a unique window to observe such patterns because their fossil
shells not only allow for species-level identifications and quantification of abundance
(Schilthuizen 2011), but can also provide accurate radioisotope dates (Pigati et al.
2010). Here we compare species turnover and accumulation patterns in comparable
temperate (Slovakia and the Czech Republic) and tropical (Malaysian Borneo) land
snail datasets. ese analyses show that while temperate communities demonstrated
significant compositional change over the modern to Late glacial maximum (LGM)
transition, tropical communities did not.
Dissimilarity in both datasets was driven by species turnover (0.74 versus 0.65 for
temperate versus tropics) rather than by differences in richness (0.13 versus 0.07).
Highly significant temporal distance decay (DD) in species composition was noted
(Fig. 1) for the temperate dataset (p << 0.0001) while no significant decay was noted
over the same period in the tropics (p = 0.28). us while over 70% of observed
similarity decay was explained by temporal distance in Slovakia/Czech Republic, less
than 10% was explained in Malaysia. AICc value comparison in the temperate data
indicated that a two-parameter exponential form (–44.1) was much better fit to the data
than a two-parameter power-law form (–25.6). Important differences were also noted
in the shape of the species–time relationship (STR). While Slovakia/Czech Republic
data demonstrate a 78% cumulative increase of species over the modern-LGM axis,
the Malaysian data accumulated a dozen fewer species over the same temporal extent.
e tropical data also exhibited a more pronounced asymptote: while cumulative
temperate species richness demonstrated a 50% increase in cumulative richness from
0.3–25 ka, tropical richness only increased 20% over the same period.
ese analyses demonstrate that while there has been continual turnover in land
snail assemblages in the temperate system, the tropical system demonstrated compo-
sitional stasis. Observed turnover in the temperate system was expected given regional
biome change from the cold and dry LGM to wet and warm modern. Such directional
change in the regional species pool is supported by extensive fossil evidence (Ložek 1964)
and is further documented by the exponential form of the temporal DD relationship
(Nekola and McGill 2014). At least some turnover was expected from the Malaysian
First evidence for long-term stasis in wet-tropics land snail
community composition
Jeffrey C.Nekola, MennoSchilthuizen, KatherineSzabo, VeronikaHorsáková and MichalHorsák
J. C. Nekola (http://orcid.org/0000-0001-6073-0222) (jnekola@unm.edu), V. Horsáková and M. Horsák, Dept of Botany and Zoology, Masaryk Univ.,
Kotlářská 2, CZ-611 37 Brno, Czech Republic. JCN also at: Biology Dept, Univ. of New Mexico, Albuquerque, NM 87131, USA. – M. Schilthuizen,
Naturalis Biodiversity Center, Leiden, the Netherlands, and: Inst. Biology Leiden, Leiden Univ., Leiden, the Netherlands. – K. Szabo, Max Planck Inst. for
the Science of Human History, Jena, Germany.
Brevia
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data, however, given known palynological changes from sea-
sonally dry to wet tropical forest over the analyzed temporal
extent (Jones et al. 2014). Yet, community similarity only
varied between 0.4–0.6 and demonstrated no significant trend
across 0.3–25 ka extents. ese similarity values are equiva-
lent to those observed between adjacent (10 km) modern karst
tower faunas at Simbaluylon and Tinahas, Malaysia (48 and
45 observed species, respectively, with 36 in common) and are
likely driven by stochastic differences between samples drawn
from the same regional pool (Preston 1962).
It is not immediately clear why land snail community
composition in the tropics has been more resilient to long-
term regional climate change than that observed for vascu-
lar plants in the same region. We hypothesize that this may
be related to the: 1) smaller habitat size required to sustain
minimally viable land snail populations – ranging down
to 10-m² areas for some microsnails (Schilthuizen 2011),
and/or 2) excellent passive dispersal abilities of many land
snails (Gittenberger et al. 2006) which allow them access to
even the most isolated refugia. us an archipelago of tiny
refugia within the karst-tower landscape may provide long-
term buffering against moderate temperature and consider-
able precipitation variability, helping maintain a uniform
regional species pool over long time scales. e temporal
turnover seen in the temperate zone, however, probably
reflects the greater total experienced temperature and precipi-
tation variation which exceeded the ability of such tiny, local
refugia to buffer regional climate change.
Lastly, even though land snail communities are among the
clearest examples known for neutral community assembly
(Schilthuizen 2011), we note that these data provide no clear
evidence for directional stochastic compositional change
(aka ‘ecological drift’ of Hubbell 2001) over time. us even
though such drift can be generated in mesocosm experiments
over short time scales (Gilbert and Levine 2017) it is unclear
that this process is important in natural systems.
Figure 1. Comparison of temporal community composition changes for central European temperate and Malaysian wet tropic land snail
communities. (Top row) Distance decay over the modern to LGM transition based on all pairwise sample comparisons. (Bottom row)
Species–time relationship across 0 (modern) to 25 ka extents.
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References
Condit, R. et al. 2002. Beta-diversity in tropical forests. – Science
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Gilbert, B. and Levine, J. M. 2017. Ecological drift and the distri-
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Gittenberger, E. et al. 2006. Molecular trails from hitch-hiking
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Hubbell, S. P. 2001. e unified neutral theory of biodiversity and
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Jones, S. E. et al. 2014. A Late Pleistocene record of climate and
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Supplementary material (Appendix ecog-03996 at <www.
ecography.org/appendix/ecog-03996>). Appendix 1–4.
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