Download Habitat Use by White-tailed Deer in a Tropical Forest

Habitat Use by White-tailed Deer in a Tropical Forest
SALVADOR MANDUJANO
SONIA GALLINA
GERARD0 SANCHEZ-ROJAS
GLORIA ARCEO
Depto. Ecologia y Comportamiento Animal, Instituto de Ecologia A.C., AP 63, Xalapa 91000,
Veracruz, Mexico.
GABRIELA SILVA-VILLILOBOS, CUCBA
Universidad de Guadalajara, AP 39-82, Zapopan 451 10, Jalisco, Mexico
Abstract: White-tailed deer in the tropical forest of "Chamela" in the state of Jalisco,
Mexico, exhibit different spatial and temporal habitat use patterns. The heterogeneity of
the understory of Chamela's tropical forest is determined by spatial (tropical dry forest
and tropical semideciduous forest) and temporal (wet and dry seasons) variations in
floristic composition, species richness and biomass, nutritional value, percentage of
deciduous and evergreen species, and life form. During the wet season, white-tailed deer
make greater use of the tropical deciduous forest. During this season the diet is less
diverse. This greater selectivity in the diet is associated with an increase in foraging area,
as greater distances are covered and the home-range is increased. In the dry period, low
water and food availability is coupled with a decrease in cover to protect against climate
and predators. White-tailed deer increases the diversity of its diet during this season. It
also increases consumption of alternative food sources and water, such as fruits and
flowers. Thus, habitat use is less selective in the dry season than in the wet season.
Key words: Habitat structure, habitat use, Mexico, Odocoileus virginianus, tropical
forest, white-tailed deer.
INTRODUCTION
White tailed deer (Odocoileus
virginianus) are found throughout all of
Mexico except on the Baja California
peninsula and in northern Sonora (Hall
1981). The species inhabits a wide variety
of vegetation types, such as temperate
forests, grassland, semi-arid land, and
tropical forest (Leopold 1965). This deer
supplements the diet of local' ethnic groups
(Mandujano and Rico-Gray 1991) and is 1
of Mexico's most important game species
(Villarreal 1995).
Most studies of this species have been
carried out in temperate forests and semiarid zones of the United States, Canada, and
Mexico (see Halls 1984). In contrast, few
studies have been conducted in the tropical
forests of Mexico, or in Central and South
America (Vaughan and Rodriguez 1994).
The present results are from a study of
white-tailed deer (0. v. sinaloae) ecology in
a tropical forest located in the state of
Jalisco, Mexico, over a 6-year period (19891995). Our objectives were to determine
basic life history information on population
dynamics, activity patterns, and habitat use
in a tropical environment noted for the
marked seasonality of its available
resources. The information contained in
this paper is based on articles (Mandujano
and Gallina 1993, 1995a, 19953, 1996;
Mandujano et al. 1994; Mandujano and
Martinez-Romero in press; Sanchez-Rojas
et al. 1997), theses (Mandujano 1992,
Sanchez-Rojas 1995, Silva-Villalobos 1996,
PROCEEDINGS
- 1997 DEERIELKWORKSHOP
- ARIZONA
Arceo 1997), and recent information which
is yet to be published. See these
publications for details regarding methods,
statistical analyses, and results discussed in
a wider context.
We appreciate field support from R. E.
Sanchez-Mantilla, L. E. Martinez-Romero,
C. Lopez-Gonzalez, D. Valenzuela, G.
Zavala, and G. Gonzalez. The following
people collaborated in the identification of
herbarium samples: F. Chiang (all groups),
M. Sousa (Leguminosae), 0. Tellez
(Leguminosae), and J. L. Vil'laseiior
(Compositae). The following people
collaborated in the laboratory analysis: L.
Barrientos, M. Barrientos, M. Castellanos,
G. Lopez, and L. Villarino. This study
received support from CONACYT
(P220CCOR-892 154, P020CCOR-903703
and 0327N9107) and SEP (DGICSA902467) projects. The UNAM's Chamela
Biological Station provided all the facilities
necessary for the successful completion of
this study.
DESCRIPTION OF HABITAT
Study Site
This study was carried out at the
Universidad Nacional Autonoma de
Mexico's "Chamela" Station for Research
and Biological Diffusion, located on the
coast of Jalisco. The Station covers an area
of 3,200 ha. The elevation ranges from 30
to 580 m, although most of the territory is
not higher than 150 m. The topography is
irregular with numerous systems of small
basins, all of which have seasonal run-off.
The greatest quantity of water falls in
September (Bullock 1986). Depending on
the amount of rainfall, there is frequently no
water in the streams by the end of the dry
season. Apart from these seasonal streams,
there are only 3 permanent rivers in a 100
km radius of the Biological Station.
Climactic Pattern
Average annual precipitation from 1977
to 1993 was 73.55 cm. Monthly
precipitation causes 2 seasons: wet (rainy)
and dry. The wet season, which lasts an
average of 126 days, begins in June, with
80% of the annual rain falling between July
and November (Bullock 1986). Twenty
percent of the annual rain falls during the
dry season, which lasts an average of 158
days. From June to July, the Trade Winds
play a role in the variability of annual
rainfall; cyclones occur during August to
October and greatly increase the likelihood
of winter precipitation (Garcia-Oliva et al.
1991).
The mean annual temperature is 25 C,
the hottest periods occurring between May
and September (Bullock 1986). From June
to November, the temperature was greater
than 30 C on an average of 23 days
(Mandujano and Gallina 1995a). From
mid-December until mid-May, temperatures
did not exceed 30 C. Insolation is highest in
April. The maximum wind speed occurs
from February to June and the minimum
from August to December. The greatest
evaporation occurs between March and June
and the least between November and
January. During the wet season dew was
present for 7-15 days and between 5-12 days
during the dry season (Gonzalez 1992).
Types of Vegetation
The dominant vegetation, covering 75%
of the surface, is tropical deciduous forest
(TDF). It is found on hills with shallow
soils; the trees reach a height of 5 to 10 m
and have a highly developed understory.
Numerous tree and shrub species lose their
leaves during the dry season (Lott et al.
1987). Some of the most common arboreal
species are Cordia alliodora (Ruiz & Pav.)
Oken, Croton pseudoniveus Lundell,
Lonchocarpus lanceolatus Benth, and
Caesalpinia eriostachys Benth. There is
also tropical semi-evergreen forest (TSF),
Habitat Use by White-tailed Deer in a Tropical Forest
Mandujano et al.
which grows along the principal streams in
deep soils. The trees reach a height of 10 to
25 m. The most common tree species are
Thouinidium decandrum (Humb. & Bonpl.)
RadIk., Astronium graveolens Jacq.,
Brosimum alicastrum Sw, and Sideroxylon
capiri A. DC. (Lott et al. 1987).
Understory Structure
In the wet and dry seasons during the
period from 1989 to 1993, understory
richness and biomass was measured in the
TDF and TSF using permanent plots. The
best represented families, genera, and
species in the understory were
Euphorbiaceae, Leguminosae, Sapindaceae,
and Acanthaceae; Acalypha spp., Croton
spp., Lasiacis ruscifolia, Coursetia
caribaea, Dicliptera resupinata,
Forchhammeriapallida, Capparis
verrucosa, and Elytraria imbricata. In the
TSF they were Euphobiaceae, Leguminosae,
Bignoniaceae, Nyctaginaceae, and
Sapindaceae; Acacia rosei, Guapira
macrocarpa, Croton pseudoniveus,
Thounidium decamdrum, Clytostoma
binatum, Paullinia cururu, and Capparis
verrucosa. During the wet season, 39% of
the species were exclusive to the TDF, 43%
to the TSF, and 18% are found in both
vegetation types.
Average species richness during the dry
season was 2 species/m2in the TDF and 4 in
the TSF; during the wet season, richness
was 9 species/m2in the TDF and 8 in the
TSF. Average biomass during the dry
season was 7 g/m2in the TDF and 18 in the
TSF, while in the wet season it was 41 g/m2
in both types of forest. There was a positive
correlation between the precipitation and
richness of both TDF and TSF and their
biomass.
Availability of Potential Food in the
Dry Season
Biomass availability for the species
which deer consume in the TDF varied
during the dry season from 2 to 12 g/m2,
depending on the year. This corresponds to
an average of 23% of the standing biomass
in the understory of this vegetation type
(Mandujano and Gallina 1995a). In the
TSF, availability was estimated at 1 to 10
g/m2for species which the deer consume;
this corresponds to an average of 9% of the
biomass for this type of vegetation.
Nutritional Value of the Vegetation
Using a proximal analysis, we found
that the nutritional value of vegetation was
greater during the wet season, as there was a
higher percentage of crude protein and
nitrogen free extract (NFE). Nutritional
value decreased during the dry season, when
there was a higher percentage of crude fiber
and total polypyenols (Silva-Villalobos
1996). Plants in the TSF have a higher
percentage of fiber, less protein, and less
NFE throughout the year. Plants in the TDF
had a high nutritional value during the wet
season and a low value during the dry
season.
Seasonal Fruit Production
Fruit production of arboreal species
tends to occur mainly from February to
early April and from July to August
(Bullock and Solis-Magallanes 1990).
Some species deer consume during the dry
season are Ficus sp., Brosimum alicastrum,
Sideroxylon capiri, Opuntia excelsa, and
Spondiaspurpurea.
Characteristics of the Spondias
purpurea Tree
Fruits from the S. purpurea are an
important source of water for the deer at the
end of the dry season because there are few
of water sources. S. pururea is a dioecious
arboreal species. The density of adult trees
is 7.5tha; approximately 50% are
reproductive female trees, 38% of which
Habitat Use by White-tailed Deer in a Tropical Forest
Mandujano et al.
produce more than 500 fruits (Mandujano et
al. 1994). The average weight of fresh f i t
is 7.5 g, and fruit production during 1991
was 14.9 kg/ha.
Chachalaca (Ortalis poliocephala)
foraging on S. purpurea has important
consequences for the deer. When
chachalacas forage, they drop many h i t s
from their trees, making them available for
the deer as well as for other terrestrial
mammals. Exclusion experiments show
that in the absence of this bird, the rate of S.
purpurea fruitfall is very low (Mandujano
and Martinez-Romero in press).
Water Availability
An estimate of the average availability
of water for the deer was obtained using
plant moisture content and the percentage of
plants that the deer were known to consume
in both types of forest during the dry
seasons fiom 1990 to 1993. In the TDF, the
average density of deer forage plants was
3 l h a (ranging from 10-56ha), while in the
TSF the average was 28iha (ranging from 450ha) (Mandujano and Gallina 1995a).
The average estimate of water in S.
purpurea fruits was 10 Liha in 1991.
HABITAT USE BY THE DEER
Biological Cycle
In the tropical forest of Chamela, the
breeding season occurs between November
and January (Mandujano 1992). Gestation
occurs throughout the dry season, between
December and June. The young are born
between June and August.
Group Size
In this habitat, the white-tailed deer do
not form large herds (Mandujano and
Gallina 1996). Solitary individuals are
frequently seen throughout the year.
Females and their offspring comprise the
most common social groups. Males are not
known to form groups. This group size
strategy is related to the availability of food,
and to the density of cover in the understory
that provides protection against predators.
Population Dynamics
Population density was estimated using
a direct count of animals on line transects.
Population density was estimated between
10 and 14 deer/km2(Mandujano and Gallina
1993, 1995b), and did not change over a 5year period. The birth rate is 1.5 fawns per
female, however, the mortality rate is high
from the fawn to yearling category.
Mortality is higher for males than for
females. We propose that the period
between May and June is the "bottle-neck"
for deer population increase in this tropical
habitat.
Feeding Habits
Using microhistological fecal analyses,
129 species of 29 families were eaten by
deer (Arceo 1997). The most important
families were Euphorbiaceae, Leguminosae,
and Convolvulaceae throughout the year,
Malvaceae during the wet and transition
seasons, and Anacardiaceae during the dry
season. The deer selected 36,55, and 44
species during the wet, transition, and dry
seasons, respectively. But on average, only
5 species represent 50% of the seasonal diet.
Acalypha spp. was the most important food
item in the wet and transition season.
Overall, Acalypha langiana,
Cardiospermum halicacabum, Coursetia
caribaea, Croton sp., Abutilon sp., Spondias
purpurea, and Ayenia micrata were the
more important species in the diet. Deer
diets became more diverse from wet to dry
season, and the plant parts consumed
changed in this period. Leaves and twigs
were the most important plant parts in the
annual diet, but in the dry season fruits and
flowers, particularly fruits of red mombin
(Spondias purpurea), constituted 30% of its
diet. Overall, shrubs and vines were the
Habitat Use by White-tailed Deer in a Tropical Forest
Mandujano et al.
most important life forms in the diet yearround, with trees being most important in
the dry season. Perennial plants with
deciduous leaves were dominant in the diet
year-round. Plant species from TDF
comprised a greater percentage of the diet,
principally in the dry season, than those
species from the TSF.
Water Demand
The deer population's need for water
was estimated using the following factors:
daily water demand for 1 individual,
average weight, the percentage of each age
group represented, annual population
density, and consumption over 30 days at
the end of each year's dry season
(Mandujano and Gallina 1995~).Minimum
and maximum individual demand was
estimated at 1.9 and 3.9 Llday, respectively,
for adult deer, 1.4 and 2.8Llday for young
deer, and 0.8 and 1.7LIday for fawns.
Use of Vegetation Types
Through direct observations of deer and
pellet group counts from 1989 to 1994, we
found that the TDF is used more frequently
throughout the year than the TSF. In
particular, in the wet season the TDF is used
more during the morning hours, while in the
dry season it is used more in the afternoon.
The TSF, in contrast, is used during the
morning in the dry season and very little
during the day in the wet season. Deer
prefer the hillsides with northern exposure
in the dry season.
From 1992 to 1994, radiotelemetry of 1
male (n = 122 locations) and 1 female (n =
479) indicated that females preferred
hillsides more than areas near streams
(Shchez-Rojas 1995). Specifically, the doe
favored hillsides facing NE or NW during
the wet season and SW during the dry
season. The male, on the other hand, made
less use of hillsides facing NW and SE and
preferred low areas.
Activity Patterns
The radiotracking of 2 deer provided the
following data. In the dry season, the
female exhibited more movement at dawn
(0500-0800 hours) and at dusk (1700-2000
hours). In the wet season, she remained
active throughout the day, slowing down
notably at night (2 100-0400 hours). Male
activity during the dry season was higher at
dusk and at night. The distance covered by
the female was 1.5 km/day in the dry season
and from 2.5 km/day in the wet season. The
male covered 2.5 km/day in the dry season
of 1994. Estimates of female home-range
were 11 ha during the dry season and
between 24 and 44 ha in the wet season
(Shchez-Rojas 1995). Figures for the male
were 26 ha in the dry season of 1994.
Predation
At Chamela, the jaguar (Panthera onca),
puma (Puma concolor), and ocelot
(Leoparduspardalis) are the principal
predators of white-tailed deer (LopezGonzalez et al. 1995). Like other studies
(Main et al. 1996), it is very probable that
the deer's habitat use is influenced by the
risk of predation. Tracks of these felines are
common along the streams of the study
area.
IMPLICATIONS
Results indicate that the deer's foraging
strategy during the wet season is to make
greater use of the TDF because of its high
nutritional value (higher percentage of
protein and NFE and less fiber), greater
richness and increased production of
biomass of understory species as compared
to the TSF. During this season the diet is
less diverse, which indicates that the deer
selects fewer species, principally those of
the Euphorbiacea, Convolvulacea, and
Leguminosae families, to cover its
nutritional requirements. Deer get more
energy and nutrients from these species,
Habitat Use by White-tailed Deer in a Tropical Forest
Mandujano et a/.
thus permitting the accumulation of fat
reserves for the mating season and for the
critical dry season. This greater selectivity
in the diet could be associated with an
increase in the foraging area, as greater
distances are covered and the home-range is
increased.
In the dry period, low water and food
availability is coupled with a decrease in
cover to protect against climate and
predators. The deer's strategy is to select,
.from low species richness and biomass,
those plants and plant parts which are more
nutritious and that have lower
concentrations of fiber. Thus, the whitetailed deer increases the diversity of species
and families in its diet during this season. It
also increases consumption of alternative
sources of nutrients and water, such as h i t s
and flowers, especially Spondiaspurpurea,
Ficus spp., and Brosimum alicastrum.
Thus, habitat use is less selective in the dry
season than in the wet season. Apparently,
the distribution of fruiting trees plays a role
here. During the dry season, deer show a
clear preference for hillsides with northern
exposure where the solar radiation is lower
and humidity higher. Also, deer cover less
distance, decreasing their home-range which
could be a strategy to diminish energy
demand and protect against predators.
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