ECOLOGICAL NICHE MODELING OF THE SOUTH AMERICAN LATE PLEISTOCENE MEGAFAUNA: EXPLORING REGIONALIZATION AND CONNECTIVITY

1. ECOLOGICAL NICHE MODELING OF THE SOUTH
AMERICAN LATE PLEISTOCENE MEGAFAUNA:
EXPLORING REGIONALIZATION AND
CONNECTIVITY
L. Varela1,2* , P.S. Tambusso1,2, L. Clavijo1,2, C. Lobato1,2,
T. Núñez1,2, and R.A. Fariña1,2
1Departamento de Paleontología, Facultad de Ciencias, Universidad de la República, Iguá
4225, 11400, Montevideo, Uruguay
2Servicio Académico Universitario y Centro de Estudios Paleontológicos (SAUCE-P),
Universidad de la República, Departamento de Canelones, Santa Isabel s/n, 91500,
Sauce, Uruguay
*luciano.lvr@gmail.com

2. THE LATE PLEISTOCENE
SOUTH AMERICAN
MEGAFAUNA AND THEIR
DISTRIBUTION PATTERNS
• The late Pleistocene megafauna of South America represents a
unique assemblage of large mammals that occupied almost all
parts of the continent. These species were important parts of their
ecosystems, with roles related to seed dispersal, nutrient transport,
and biotic connectivity, among others. Most of these taxa became
extinct at the end of the Pleistocene, coinciding with the
establishment of warmer climatic conditions and the expansion of
human populations in the continent.
• Previous studies have shown that the distribution of many
megafauna taxa agree with biogeographic provinces defined for
extant taxa, as well as the existence of limits coinciding with the
vegetal formations predicted for the Pleistocene and migratory
routes in the continent. Some examples are shown in the right.
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Gallo et al. 2013
Scillato-Yané et al. 2005
Prado & Alberdi 2013

3. ECOLOGICAL NICHE MODELS
OF LATE PLEISTOCENE SOUTH
AMERICAN MEGAFAUNA
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• Previous studies using Ecological Niche Models (ENMs)
have focused in specific taxa or clades to explore their
climatic preferences and changes in distribution during
the Pleistocene and before their extinction at the
Pleistocene-Holocene boundary. Some examples are
shown in the right.
• Here, we explore the climatic preferences and potential
distribution of 39 herbivorous taxa (including
Artiodactyla, Perissodactyla, Proboscidea,
Notoungulata, Litopterna, and Xenarthra) belonging to
the late Pleistocene megafauna using Ecological Niche
Models (ENMs) and connectivity algorithms to explore
regionalization and connectivity.
Varela et al. 2018
Araújo et al. 2021
Villavicencio et al. 2019

4. SPECIES OCCURRENCES AND
PALEOCLIMATIC DATA
• 39 herbivorous taxa:
Artiodactyla: Hemiauchenia paradoxa, Lama guanicoe,
Palaeolama major, Palaeolama weddelli, Vicugna vicugna,
Morenoelaphus brachyceros.
Perissodactyla: Equus neogeus, Hippidion principale,
Hippidion saldiasi, Tapirus terrestris.
Proboscidea: Cuvieronius hyodon, Notiomastodon platensis.
Notoungulata: Toxodon platensis, Mixotoxodon larensis.
Litopterna: Macrauchenia patachonica, Xenorhinotherium
bahiense, Neolicaphrium recens.
Xenarthra: Lestodon armatus, Mylodon darwinii,
Glossotherium robustum, Scelidotherium leptocephalum,
Catonyx chilensis, Catonyx tarijense, Catonyx cuvieri,
Valgipes bucklandi, Nothrotherium maquinense,
Diabolotherium nordenskioldi, Eremotherium laurillardi,
Megatherium americanum, Doedicurus clavicaudatus,
Neosclerocalyptus paskoensis, Propraopus sulcatus,
Holmesina occidentalis, Holmesina paulacoutoi,
Pampatherium typum, Pampatherium humboldtii,
Panochthus tuberculatus, Glyptodon reticulatus,
Glyptotherium cylindricum.
• Data of occurrences assigned to the last glacial
maximum (LGM) at ~33.0 to 19.0 ka (Clark et al. 2009)
were obtained from a review of the literature and from
the Paleobiology Database (paleobiodb.org).
• 19 Bioclimatic variables obtained from the PaleoClim
database (www.paleoclim.org).
Geographic distribution of the
occurrence records of all studied taxa.

5. ECOLOGICAL NICHE
MODELS
• The models were constructed for the LGM using occurrence records
between 13 and 40 ka, assuming that the species were also present
during the LGM.
• Model results were further evaluated using the R package
Phyloclim (Heibl and Calenge 2013). Niche Overlap between
the species was evaluated using the statistics D and I (Warren
et al. 2008) and Predicted Niche Occupancy (PNO) profiles
(Evans et al. 2009) for the different species in relation to each
environmental variable were created. Furthermore, we performed
kmeans cluster analyses to explore groupings of taxa based on
climatic preferences.
• Model performance was evaluated using the area under curve
(AUC) statistic. An AUC value of 0.5 indicates a random prediction,
whereas closer to 1 values indicate better predictive ability. A
jackknife procedure was used to assess the contribution of the
variables used in the modeling process.
• The potential distribution of fossil xenarthrans was reconstructed
by ecological niche modeling using the software MAXENT v.3.4.4
(Phillips and Dudik 2008).

6. CONNECTIVITY MODELING
ALGORITHMS
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• For each taxa, we used the ENMs resulting viability raster as source
layer, while the Terrain Ruggedness Index (TRI; obtained using QGIS
from a DEM) was used as the resistance layer.
• Using QGIS, the results of each taxa where then standardized, and
a composite layer was created for each cluster recovered in the
previous analysis. This approach allowed for the visualization of
potential common routes and overall habitat connectivity among
taxa for each cluster.
• The landscape connectivity was assessed using the Omniscape
algorithm (McRae et al. 2016) implemented in Julia Programming
Language. Omniscape.jl is built on Circuitscape.jl. The Omniscape
algorithm works by applying Circuitscape iteratively through the
landscape in a moving window with a user-specified radius.
• All the analyses were
carried out using
ClusterUY (Nesmachnow
S., Iturriaga S. 2019; site:
https://cluster.uy).

7. RESULTS - ECOLOGICAL NICHE MODELS
• Kmeans Cluster analyses revealed two possible
configurations (k =3 and k =4) based on the elbow
method.
• Overall, all the models showed considerably high AUC
values. Some specific cases showed relatively low values
(~0.75), mostly related to the scarce number of available
record for those taxa.
Results of the kmeans cluster analysis showing alternative configurations using 3 or 4 clusters.
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8. RESULTS - ECOLOGICAL NICHE MODELS
• Composite PNOs of each cluster show
differences among them in relation to
temperature and precipitation.
• Cluster 1 is mainly composed of taxa found
in the Brazilian Intertropical Zone, with some
occurrence also in the Río de la Plata region
and the Argentinian Mesopotamia. The PNOs
show preferences for warmer and drier
habitats, but some peaks are also visible for
colder and wetter habitats.
• Cluster 2 is mostly composed of taxa found
in the Río de la Plata region. The PNOs show
preference for colder and wetter habitats.
• Cluster 3 is composed of widely distributed
taxa mostly occupying the Northern regions
of South America. The PNOs show
preferences for warmer and drier habitats.
• Cluster 4 is majorly composed of Andean
taxa. The PNOs show preferences for
considerable warm and dry environments,
although the inclusion of Hippidion saldiasi
is reflected in higher suitability in colder
habitats.
Composite PNOs for each cluster showing the response to two bioclimatic
variables.
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9. RESULTS - CONNECTIVITY ANALYSES
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• Cluster 1 • Cluster 2
• Composite layers showing landscape connectivity results for each cluster obtained in the previous analyses. High
(lighter) values mean current flow is channelized while low values mean current is impeded.
• Cluster 3 • Cluster 4

10. DISCUSSION
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• The results support the existence of a clear
regionalization of large herbivorous mammals during
the late Pleistocene related to climatic preferences.
• The main division observed is in line with previous
suggestions, showing groups of taxa more associated
to southern regions and groups of taxa related to more
tropical regions.
• A group of taxa commonly found in the Brazilian
Intertropical Region shows a strong connection to the
southern Río de la Plata region, clearly showing the
connectivity between some of the recognized
ecoregions.

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• The connectivity analyses showed potential connections
between the different regions.
• In particular, for the taxa found both in the Río the la
Plata region and the Brazilian Intertropical region, the
results showed strong canalization of the current on the
Atlantic coasts. These results would indicate that these
now-submerged lands could have functioned as
corridors that allowed the intermix of northern and
southern taxa.
• For taxa mostly recorded in the Andean region, a clear
corridor was recovered along all the Andean Mountains,
indicating a strong connection of northern and southern
regions mainly through the Pacific coasts.
DISCUSSION

12. SUMMARY
• The geographic projections of the climatic niches
estimated for these taxa support the
regionalization of faunas coinciding with
previously proposed ecoregions in South America
during the LGM.
• Taxa can be grouped according to their climatic
preferences, showing closely related taxa with
different preferences regarding temperature and
humidity.
• These ecoregions would be connected through
certain corridors, which would allow the intermix
of some taxa and the occurrence of, for example,
mixed faunas including northern and southern
taxa.
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13. THANK YOU
Luciano Varela
luciano.lvr@gmail.com.com
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