DISCUSSION
Our results show that the
occurrence of the three Amazonian canid species C. thous,S. venaticus and A. microtis may be negatively affected by
climate change in the future, with losses of their entire suitability
area in South America from 15% to 91% and in the Brazilian Amazon
losses ranging from 18% to 56%. However, the effects can be
differentiated between the species according to their ecological demands
and the environmental variables that can modulate their climatic niches.
For C. thous and S. venaticus , the climate variables and
those associated with anthropogenic disturbances that modulate their
niches today, may not act in the same way in the future. Thus, the rapid
environmental changes might function as ecological traps for these
species (Robertson and Hutto, 2006), and in the future they may no
longer survive in most of the areas considered suitable for them today.
Among the three species A. microtis has the most restricted
distribution confined to the Amazon Forest and the one with the least
projected loss of suitable climatic areas in the future. Apparently,
this species is a specialist in forest habitats, in particular in
continuous and preserved forest (Michalski, 2010; Leite-Pitman and
Willians, 2011). Probably, the loss of suitability for this species is
directly related to the loss of deforestation and forest degradation
(Rocha et al., 2020). In addition to the distribution of the climatic
niche of this species mainly coinciding with the most conserved regions
of the Amazon Forest, our results showed a strong influence of Forests
and Water on the occurrence of A. microtis . The association of
this species with watercourses is also known from the literature and is
suggested by interdigital membranes which may be an adaption for moving
on soft soil (Leite-Pitman and Williams 2004; Castelló, 2018). Although
the proximity to urban areas was not one of the main variables
determining the occurrence of A. microtis , we found that this
variable was negatively related to its occurrence, corroborating its low
tolerance to disturbed habitats (Michalski, 2010; Leite-Pitman and
Williams, 2011; Rocha et al., 2020). Thus, the loss of suitability areas
in the future for A. microtis cannot be related to the ecological
trap theory. This species will probably no longer occur in unfavorable
habitats due to its fitness for higher-quality forest habitats.
For A. microtis , one of the consequences of deforestation and
human pressure is increased hunting (Constantino, 2016), including
hunting with domestic dogs. Thus, disease transmission by domestic dogs
will pose a threat to A. microtis (Schenck and Stail, 2004;
Leite-Pitman and Williams, 2011). Our results corroborate those of Rocha
et al. (2020), who expected a loss of 30% of the A. microtisdistribution area by 2027, due to forest loss. Based on the last three
years of high deforestation rates in the Amazon (PRODES, 2021), and
using a pessimistic projection for the future, the loss of area of
occurrence of this species could be much more severe.
Considering habitat selection, an animal cannot always make the best
choice about where to live (Kristan, 2003; Stamps and Swaisgood, 2007),
but its initial choice may later affect the individual’s survival and
its reproductive success. However, the ultimate reason that determined
the choice may have not been evident when the choice was made (Hutto
1985; Kristan, 2003). In the case of altered environments in the Amazon,
it is possible that the attractiveness of these habitats by species such
as C. thous or S. venaticus , are detaching themselves from
the species’ aptitude for survival and reproduction. The preference of
these species for anthropogenic environments was evident from our GLM
analyses, where natural open areas negatively influenced the occurrence
of C. thous , while anthropogenic open areas had a positive
impact. The same was apparent for S. venaticus where
anthropogenic open areas had a positive effect on its occurrence. These
lower-quality habitats may at some point be just as attractive as
preserved native habitats. This can happen when animals whose behaviors
have been shaped by exposure to different environmental conditions in
their evolutionary history, are suddenly confronted by altered or novel
environments (Iwasa and Levin, 1995). In these situations where
impoverished environments become more attractive and ”bait” individuals,
these environments are called ecological traps (Gates and Gysel, 1978;
Robertson and Hutto, 2006).
Of the three species surveyed, C. thous appears to be the least
demanding in terms of habitat, with aptitude for open environments and a
high tolerance for anthropogenic habitats (Ferraz et al., 2010). In the
Amazon, this species is common in natural non-forest environments, such
as in areas of Canga Metalófila in Carajás, State of Pará (Carvalho et
al., 2014), or in areas of the Amazon Cerrado in the State of Amapá
(Coelho et al., 2014). In our occurrence database from the Amazon, we
had no record of C. thous in areas of continuous forest and
outside naturally open environments. On the other hand, C. thoushas been commonly recorded in areas with eucalyptus (Coelho et al.,
2014) and oil palm plantations (Mendes-Oliveira et al., 2017), and may
occur at the edge of adjacent forests, but not inside them. It also
occurs in mining areas, with a high level of degradation and locations
in the initial phase of forest recovery in the region of Paragominas
State of Pará. Interestingly, two individuals of C. thous were
recorded in 2020 within the city of Belém, State of Pará, in the Amazon
(Mendes-Oliveira, personal comm.). Cerdocyon thous does not seem
to be distributed within forests, and deforestation has favored its
expansion in the Amazon biome. The same occurred with Chrysocyon
brachyurus , (maned wolf), which expanded its extent of occurrence in
southwestern Amazonia (see Silva-Diogo et al., 2020), precisely due to
the conversion of forests into open areas in southeastern Amazonia
(Silva-Diogo et al., 2020).
Our current model showed more outstanding suitability of C. thousto more open environments, such as Cerrado and more anthropized
open areas in the Amazon, with restrictions to more forested areas, such
as in the central and northwestern portions of the Amazon. The GLM
results also corroborate the conclusion that C. thous has been
positively influenced by urban areas and anthropogenic open areas and
has been negatively by forest. However, this species was also negatively
influenced by natural open areas, suggesting a greater fitness for
anthropogenic habitats over natural areas. Although canids generally do
not show cursor adaptations like those of ungulates (Smith and Savage,
1965), C. thous has a more cursorial form than the other two
canid species studied in this research (Penrose, 2019). Longer limbs
favor more extended travel, especially in open areas. Faced with a
scenario of degradation and deforestation, this may be a morphological
adaptation that favors the entry of this species into degraded,
previously forested environments. Another characteristic that confers an
advantage to the ecological plasticity of C. thous , aboutA. microtis and S. venaticus in the Amazon, is its greater
tendency to omnivory. The ability of this species to have a poor or
meatless diet for long periods, feeding opportunistically on what the
environment offers (Macdonald and Courtenay, 1996; De Oliveira, 2009),
allows it a more remarkable ability to thrive in a broader range of
backgrounds and conditions. Considering all these characteristics, we
would imagine that the deforestation of the Amazon Forest has been
favoring C. thous . However, in the long term, this species may be
be “baited” by lower-quality environments, reducing its success and
leading it to extinction in certain areas in the future.
Considering our future projections of climate suitability for C.
thous , we observed a significant loss of suitable areas, especially in
regions already open or currently degraded by anthropogenic action,
mainly in the southern limits of the Amazon Forest and the northeast of
this biome. These climate niche loss projections suggest that
impoverished environments currently suitable for C. thous may not
perpetuate in the future. Thus, these new anthropogenic environments may
be working as an ecological trap for C. thous in the Amazon.
The same may happen with S. venaticus . This species is considered
rare (De Moura Bubadué et al., 2016), and occurs in forest habitats and
forest edges (Zuercher et al., 2005), open areas such as savanah
(Zuercher, 2001), and altered habitats (DeMatteo and Loiselle (2008).
Despite not being a habitat specialist, S. venaticus is the most
carnivorous canid in South America. And this is due to the presence, in
individuals of this species, of a large zygomatic arch, a short snout
with a reduced number of molars and a pointed lower first molar (LM1),
important adaptations for hypercarnivory, which increases the efficiency
of meat consumption (Ewer, 1973; Van Valkenburgh and Koepfli, 1993;
Beisiegel and Zuercher, 2005; De Moura Bubadué et al., 2016)
Thresholds for the occurrence of S. venaticus appear to be less
restrictive than for A. microtis but more stringent than forC. thous . DeMatteo and Loiselle (2008) mention that 20% of the
potential distribution areas of S. venaticus were associated with
degraded areas, using land-use data from 1992 to 1993. However,
Michalski (2010) recorded S. venaticus only in continuous regions
of Forest, even applying an effort using camera traps in fragments
adjacent to continuous areas. In our study, the current model showed
broad distribution suitability in South America for this species, but
with a significant loss in the future (the most extensive loss among the
three species), especially in the Amazon region. The future loss of
climatic niches in the Brazilian Amazon is concentrated both in forest
areas and areas already anthropized, indicating that this species may
suffer from the loss of high and low-quality habitats. However, the GLM
indicated that S. venaticus is positively influenced by forest,
urban areas, and anthropogenic open areas. This suggests that S.
venaticus may also be involved in an ecological trap when it chooses
lower quality habitats that may not be enough to maintain its survival
in the future. However, unlike C. thou , S. venaticus also
uses forest habitats, which allows it to survive in areas that can be
protected in the future in the Amazon.
Evolutionarily seen, the climate has been a more decisive factor than
competition in explaining morphological variation and habitat options in
canids (De Moura Bubadué et al., 2016). They showed that the skull
morphology of A. microtis and S. venaticus is more related
to warm, humid, and less seasonal environments than C. thous . The
use of different habitats and different diets reduces competition
between them. In this way, the coexistence of these species can be
compromised not by competition between them but, on the contrary, by
differences in climatic adaptations and habitat options, as our results
show.
Ecological traps occur when species erroneously choose niches where
their suitability is lower than in others after changes in the
environment (Robertson et al., 2013). Considering the evolutionary
history of species, environments altered by human actions could provide
false clues to their adaptation (Sclaepfer et al., 2002). In the medium
and long term, these ecological traps can lead to significant decrease
or even extinction of populations in these habitats before adaptation to
the new modified environment has occurred (Hale and Swearer, 2016). ForC. thous and S. venaticus , we believe that rapid changes
in landscapes (habitat degradation) will lead to “wrong choices” for
environments that will soon have large climatic variations, leading
these species to be trapped in these ecosystems, without time to adapt
to them.
Further, both S. venaticus and A. microtis appear to be
forest-dependent and must rely on the goodwill of decision-makers to be
maintained in the future. However, even though C. thous is least
dependent on the Amazon Forest, this species is probably the one that
will be most affected in the future due to the ecological traps that the
region has offered. Speothos venaticus , can also suffer from the
same process, but if the forest is maintained, the impact on this
species can be less intense. Using the canid species as a model, we
could deeply investigate these ecological effects that can affect a
large part of the Amazonian fauna in the current scenario. The future
perspectives for preserving terrestrial vertebrate fauna in this region
are pretty pessimistic. When it comes to the conservation of
impoverished regions in the Amazon, the theory of ecological traps must
be studied and discussed at the same level that habitat loss is
considered a decisive criterion for biodiversity threat.