DISTRIBUTION, HABITAT ASSOCIATION, AND FACTORS DETERMINING ASSEMBLAGE COMPOSITION OF MAMMALS IN THE PARAGUAYAN CHACO by DANIEL MARC BROOKS, B.S. A THESIS IN BIOLOGY Submitted to the Graduate Faculty of Texas Tech University in Partial Fulfillment of the Requirements for the Degree of MASTER OF SCIENCE Approved Accepted May, 1993
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DISTRIBUTION, HABITAT ASSOCIATION, AND FACTORS
DETERMINING ASSEMBLAGE COMPOSITION OF
MAMMALS IN THE PARAGUAYAN CHACO
by
DANIEL MARC BROOKS, B.S.
A THESIS
IN
BIOLOGY
Submitted to the Graduate Faculty of Texas Tech University in
Partial Fulfillment of the Requirements for
the Degree of
MASTER OF SCIENCE
Approved
Accepted
May, 1993
ACKNOWLEDGMENTS
I remain indebted to my committee chairman, Richard Strauss. His
support and encouragement attributed tremendously to a fruitful
learning experience during graduate school. Likewise, my gratitude is
extended to committee members Clyde Jones and Fred Bryant for conveying
their enthusiasm with regards to this research.
The companionship of numerous individuals in Paraguay, including
Eddie and Sonja Mueller, the Unger family, Chris Yahngtze, Mamila
Gammarra de Fox, Flavia Colman, Chaco Solar caballeros (Eduardo and
Carlo), and some of the local Mennonites is hardly forgotten. Thanks
to my immediate family, Richard, Claire, Lisa, and Greg, for mutually
supporting my pursuit, and to catherine Mueller for putting up with me
through graduate school.
Numerous Paraguayan government and non-government organizations
supported my research in Paraguay in more ways than one: Ministerio de
Agricultura y Ganaderias (Ministry of Agriculture), Servicio Forestal
Nacional (National Forest Service), Inventario Biologico Nacional
(National Biological Inventory), Cento de Datos para la Conservacion
(Conservation Data Center), and Fundacion Hoises Bertoni (The Moises
Bertoni Foundation). Financial Support was provided by Dr. Kurt
Benirschke and the Foundation for Endangered Animals. Local logistics
were provided by the Zoological Society of San Diego's Center for the
Reproduction of Endangered Species through support of Proyecto Tagua
(The Tagua Project).
11
TABLE OF CONTENTS
ACKNOWLEDGMENTS
LIST OF TABLES
LIST OF FIGURES
I I I I I I I I I I t I I t I I I I I I I I I I t I I I t I I I I I I I I I f I I I I I I I I I I I
I I I I I I I I I I I I t I I I I I I I t I I I I I I I t I I I I t I I I I I t I I I I I t t I I I I
omnivore/carnivore, carnivore, small herbivore, and large herbivore),
scores {calculated using the first principle component, which accounted
10
for 88% of the total variation among the five variables), and sizes of
each species. Differences between the first principle component scores
for each species pair represent size differences (Table 3). If
similar-sized guild members were not encountered during the same month
for 12 months of the year. this would suggest that temporal allocation
occurred.
Prey abundance could not be assessed quantitatively due to
methodological shortcomings. However, one predator in this study, the
jaguar, relied primarilY upon mammalian prey present within the study
site. Jaguar activity was paired with activity of various potential
prey items across time to test for significant association, again using
Spearman rank correlations using STATGRAPHICS (STSC, 1986).
11
Table 1. Guild assignments and sizes (based upon principal component scores) of species present within Estancia Toledo, ranked from most to least active.
Paraguayan Pampas Fox 2.85 Omnivore/carnivore 0.30 (L)
12
Table 1 (Continued).
* ActivitY is ranked from least to most active and is the annual mean relative activity for each species.
+ Due to confusion regarding taxonomic designation of hairy armadillo, the size value assigned (-1.81) was based upon that of the similar-sized three-banded armadillo.
Key for size classes: S • small; M • medium; L • large.
13
Table 2. Pearson product-moment (upper aatr ix) and Spearman rank (lower matrix) correlations between paired abiotic variables.
TEMPERATURE RAINFALL CLOUD COVER WIND VELOC.
TEMPERATURE 0.399 0.117 0.256 0.199 0.717 0.423
RAINFALL 0.399 0.640 0.582 0.185 0.025 0.047
CLOUD COVER 0.067 0.703 0.331 0.824 0.020 0.294
WIND VELOCITY 0.182 0.527 0.296 0.545 0.081 0.326
------·
• The upper values represent coefficients and the lower values represent significance levels.
14
Table 3. Size difference values between pairs of species sharing the same guild.
1. Est. Madregadda 2. Est. Ferr~r 3. Felix Zaracho 4. Lag. Pirizei 5. Est. Fort. Toledo 6. Filadelfia 1. Loma Plata 8. Lag. Por6 9. Est. Amalia 10. Lag. capit'n 11. Rio Negro and Ruta Trans-chaco 12. Fort. Zalazar 13. Mscl. Estigarribia 14. Tte. Ochoa 15. 60 km N of Fernheim 16. Fort. Carlos A. L6pez 17. w of Lag. Frente Dos 18. Tte. Martinez 19. Cerro Le6n 20. Est. San Jos6 21. Pa1mar de las Islas 22. capt. Pablo La Gerenza 23. Tte. Picco 24. 23 km S Tte. Picco
Figure 1. A map of Paraguay with numbered localities from the Chaco identified in the gazetteer.
17
' f
Nueva A nci6n 23 18 17
1 14 24 Dpto. Alto
Dpto. Boquer6D
100 km. 1--------------------1
Paraguay
E
Dpto. 1
President
Figure 2. A map of the Chaco deo1ct1n2 transect routes traveled {numbers represent localities from Figure 1).
18
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3
CHAPTER III
RESULTS
Distribution and Habitat Association
The first paragraph in each of the following species accounts
summarizes habitat association and locality information from the
Redford and Eisenberg (1992) synopsis. In situations where localities
bordered the Chaco (such as delineating rivers), a range representing
minimum and maximum values was given. The second paragraph contains
new information on locality records, range increases, department
records, and Chaco records for the Paraguayan Chaco, whereas habitat
association records are for the species throughout its range. All
information is chronologically ordered by locality, and is generally
given as follows: numbers of specimens; condition (live, roadkill,
with increased collared peccary activity (n•12, r•0.853, P•0.005).
37
I I
l ~ ...
I I
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-12
--6
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.J
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~~ · ~ J n jso ~t g S=d ~
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~ T I 1 -1
~ ~4 f r-·-r l
~r g [:j 12 .~l ' I ~ 1 jE ~ j c~t----~----~~ ----~~-----~L---~~0
Spring Summer Fall Winter
Figure 4. Seasonal changes in species richness (numbers of species), temperature (Celcius), rainfall (rom), cloud cover (degree), wind velocity (degree), and a suite of all four factors (degree). Box plot lines measure values for each month during different seasons.
Mon1hs 9 Abiotic Nte 0 Armacilo ·b Tapir B Peccary
3.0
2.5
2.0
1.5
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>-~ .. > .. ~ 0 <
>-~ "''j
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figure 5. The influence of temperature, rainfall, and a suite of abiotic factors upon activities of different species.
39
8
8
4
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10
8
8
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2
HAIRY ARMADILLO - S )-BANDED ARMADILLO - S YELLOW ARMADILLO - M LESSER ANTEATER - M GIANT ANTEATER - L
1 2 3 4 5 6 7 8 8 10 11 12
SEPTEMBER '89 - AUGUST '90
0 LESSER GRISON - S g GEOFFROY Is CAT - M B JAGUARUNDI - M ;; PUMA - L • JAGUAR - L
2 3 4 5 8 7 8 8 10 11 12
SEPTEMBER '89 - AUGUST '90
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COLLARED PECCARY - S CHACO PECCARY - M DEER - M TAPIR - L
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SEPTEMBER '89 - AUGUST ' 90
CAVY - S ~ TUCO-TUCO - M MARA - L ~ NUTRIA - L •I-
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2 3 4 5 8 7 8 8 10 11 12
SEPTEMBER '89. - AUGUST ' 90
Figure 6. Temporal distribution of species represented in five guilds.
40
CHAPTER IV
DISCUSSION
Distribution and Habitat Association
Six (28%) of the 28 recorded species were not found within
Estancia Toledo during this study (Table 1). However, 87 new
localities were recorded for 25 species, 26 range extensions were
recorded for 23 species, and 17 department records were tallied for 14
species. Only one new record, the nutria, was confirmed for the
Paraguayan Chaco. Although new localities were recorded for other
species (such as the dwarf red brocket deer, Mazama r~na> not
occurring within the Paraguayan Chaco, insufficient evidence was
obtained to verify species identifications. Eighteen new habitat
associations were recorded for 24 species. Wetzel and Lovett (1974)
collected mammals during the late winter and early spring of 1972,
primarilY from localities 12 (Zalazar) and 14 (Tte. Ochoa) of Figure 1,
and made remarks on localities, new records, habitats, rare species
documentation, and taxonomy.
Ea.Q.tMs _ _D_etermining_comPQS..i tion
Seasonality
The results of this study suggest that austral seasons are not
characterized by individual changes in temperature, rainfall, cloud
cover, or wind velocity, but rather by a correlated suite of all four
of these factors. Mammalian species richness did not change from
41
season to season. However, because there appeared to be a distinct wet
season (summer and fall) and dry season (winter and spring) (Figure 4),
Kruskal-Wallis tests were used to determine whether variation in number
of observed species occurred between wet versus dry seasons. Although
rainfall (TS•6.587, P•0.010), cloud cover (TS•5.115, P•0.024), and the
suite of all four factors (T.S.•8.3078, P•0.004) were significantlY
different between wet and dry seasons, species richness did not change
seasonally. Moreover, species activities characterized by seasonal
changes were tested separately for each individual species, and again
no results were significant. These results differ from those of
O'Connell (1989), who found that populations of small mammals
fluctuated in response to seasonal variation. Differences arising may
have been attributed to three different seasons in the Venezuelan
Llanos (dry, early wet. and late wet), or due to my study focusing
primarilY upon large mammals, for which different census methods were
used.
Abiotic Factors
Since only five (231) significant correlations were found with
individual abiotic factors (Figure 5), this would suggest that
individual abiotic factors were not significant in structuring the
assemblage as a whole. Similarly, only three {13%) significant
correlations were found with the suite of abiotic factors, suggesting
that a combination of these factors was also not significant in
structuring the assemblage as a whole. The fact that no significant
42
correlations were found with cloud cover or relative wind velocity
suggests that these factors are not as deterministic in structuring the
assemblage as are temperature, rainfall, and all abiotic factors
combined. Results suggest that gray brocket deer and crab-eating
raccoons are more active during lower temperatures, tapirs are more
active during both lower rainfall and a lower suite of weather
activity, and collared peccaries are more active during a lower suite
of weather activity; yellow armadillos are more active with higher
temperatures, higher rainfall, and a higher suite of weather activity.
OWen (1990) found that annual temperature range and inter-monthlY
precipitation (with negative and positive coefficients, respectively)
were significant predictors of Texas carnivore diversity. However, it
is possible that a temperature decrease will increase thermoregulatory
activity due to metabolic constraints, thus the reason for a higher
relative activity was possibly due to more evidential encounters.
Aquatic environments in this area of the Chaco are not common. Tapirs
rely largely upon tajamars (temporary, man-made ponds), which vary
extensively in size and ability to contain water. It is likely that,
as the tajamars begin to dry uP, tapirs will increase traveling time to
locate tajamars that contain water. The fact that sightings of yellow
armadillos correlated significantly with two different abiotic factors
and the suite of all abiotic factors suggests that activity of this
species may be largely influenced by abiotic elements.
43
Temporal Allocation of Similar Guild Members
When all mammals in this study are considered, temporal allocation
of species which share similar resources is not significant in
determining assemblage composition (Figure 6). However, preliminary
analyses suggest that large-herbivore composition is tied into temporal
resource allocation, although this may be an artifact caused by
decreased encounters of members of this guild during warmer months (see
abiotic factors section). Similarly, small herbivores were not
encounterd simultaneously for 11 months of the year. Perhaps these
results reflect plant resource seasonality; granivore composition has
been shown to be influenced by seasonal variation in seed production
(Davidson et al., 1985). Reasons for carnivores not being encounterd
simultaneously for 11 months of the year may be associated with
seasonal territorial shifts in ecological time (Rabinowitz et al.,
1986) or character displacement in evolutionary time (Dayan et al.,
1990).
Prey Activity
The results of this study suggest that prey activity does
influence predator activity. However, the preliminary nature of these
results cannot be overemphasized, as sample sizes were small. The
observation that jaguar activitY correlates highly significantly with
collared peccary activity is similar to the findings of Crawshaw and
Quigley (1991). They found that jaguar had preyed predominantly upon
peccaries and capybaras in the Pantanal wetland, part of which
44
comprises the northeastern habitat of the Chaco. Capybaras are large
histricognath rodents which were absent from Estancia Toledo. However,
the large histricognaths that were present (nutrias and lesser maras)
approached significance (P•0.057 and P•0.066, respectively) when
correlated with Jaguar activity.
45
CHAPTER V
CONCLUSIONS
Data were collected for one year in the Paraguayan Chaco to: (1)
report new geographic localities, range extensions, and habitat
associations for mammals of the Paraguayan Chaco; and (2) investigate
the effects that seasonality, abiotic factors, temporal allocation of
guild members, and prey activity have on shaping mammalian species
composition.
Eighty-seven new localities were recorded for 25 species, 26 range
extensions were recorded for 23 species, 17 department records were
made for 14 species, and one record was confirmed new for the
Paraguayan Chaco. Eighteen new habitat associations were recorded for
24 species. Mammalian species richness did not change from season to
season, or between wet and dry seasons. Neither individual abiotic
factors, or a suite of abiotic factors seem to be significant in
structuring the assemblage as a whole. Preliminary analyses suggest
that temporal allocation influences herbivore composition (and perhaps
carnivore composition).
In conclusion, the mammalian assemblage in this study is most
likely structured by multiple ecological components, rather than any
single factor. This is not surprising considering the diverse array of
organisms that survive and reproduce in the stochastic and
unpredictable Chaco. Presence of species inhabiting this
environmentally fluctuating biome suggests tenacity on an ecological
scale.
46
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