Space use by giant anteaters in a protected area within human‐modified landscape

Blog written by Alessandra Bertassoni. Read the full article here.

Shaggy, toothless, great snout and slow… These are common adjectives applied to the Giant Anteater – the largest anteater species in the Neotropic. This is a species that attracts curiosity, as well as having gaps in our knowledge of its ecology. Despite its large distribution (from Honduras to southern South America), it can be locally rare or very threatened in some areas (e.g. Central America and at the south of its distribution).

Numerous risks threaten the persistence of populations, such as wildfires, poaching, conflicts with dogs, road-kills, fragmentation, and habitat loss – these last two are the major threat to populations. To try to preserve natural habitats, countries have adopted the creation and maintenance of protected areas. On one hand, this is a good conservation strategy in times of huge changes to global systems – mostly driven by intensive human activities. On the other hand, some protected areas and their communities are immersed and isolated in human-modified landscapes. Large mammals require extended space, and the borders of the protected area are often bypassed.

This is the background of our study – “Space use by giant anteaters (Myrmecophaga tridactyla) in a protected area within the human‐modified landscape”. Our work took place in the Santa Bárbara Ecological Station (SBES), a protected Cerrado biome remnant (27 km²) surrounded by human-modified landscape in the State of São Paulo, Southeastern Brazil (Figure 1).

Figure 1: Santa Barbara Ecological Station (SBES, black polygon) and its surroundings in Southeastern Brazil. The green polygon is a Pinus sp. Plantation, the red traces are roads and Aguas de Santa Barbara municipality is represented as a light orange diamond.

This area is considered to have high biological importance due to its typical Cerrado vegetation. However, it is surrounded by pasture, sugarcane, exotic timber plantations (green dash line, Figure 1), and urban zones. It is also divided by a road network (red dash line, Figure 1). There is a resident population of giant anteaters within the SBES. We hypothesized that they would be highly dependent on the natural features of the protected Cerrado remnant because of their extreme specializations and habitat requirements. We also predicted that their home ranges will be primarily located within the SBES and the resources inside will be more used than the surroundings. Finally, we predicted that home ranges will overlap by more than 50% due to the small size of the protected area. This was a pioneer study of giant anteaters in a highly human-modified area.

To pursue these ideas it was necessary to track giant anteaters in the SBES and surrounding area. This species needs to be captured actively, as methods such as cage traps or baits are ineffective. Therefore, the team has to be in the field to search, find and catch giant anteaters.

In 2015, we spent three months in the SBES and its surrounding area. We covered approx. 12,000 km (three field campaigns) and we succeeded in capturing eight giant anteaters; four females (F) and four males (M). We fitted them with GPS-harnesses (see Figure 2).

Figure 2. A tracked giant anteater with GPS harness in the Santa Barbara Ecological Station, Southeastern Brazil.

For a few months (10 – 147 days, 91 on average), we were able to record 13,170 locations of the tracked individuals (Figure 3). This enabled us to record a great deal of interesting ecological data. Five giant anteaters (2 F and 3 M) remained almost exclusively inside the SBES and the other three (F1, M2, and M4) had more than 20% of their locations recorded outside of it. This gives us some indication that the SBES area and its requirements are not enough alone to accommodate this population. Residing outside of the protected area could be the best choice for individuals that require more space or are searching for specific resources which are too many exploited or limited within the SBES.

Another clue was the increasing trend in the home-range area of the two males (M2 and M4) to leave the SBES. From a conservation genetic perspective, individuals that leave a population to reach another can be considered propagules that contribute to the genetic pool. But, in a human-modified landscape, leaving protected areas is too risky, especially in a place that has more than one road.

In the two years that we spent in the study area, we found giant anteaters, deer and other animals killed by collisions with traffic. We predicted a great deal of overlap between individuals due to the SBES size, and we reported that dyads of opposite sex presented larger area-overlap than same-sex dyads, using two space-sharing indexes. However, this is not breaking news. Much more elucidative data came from the analysis of combined trajectories. This revealed proximity events in five dyads of opposite sexes and a male-dyad.

Figure 3. Giant anteaters locations inside the SBES and surroundings, Southeastern Brazil. M = male and F = female.

.What does this mean? Proximity events could indicate higher levels of coexistence than previously reported for this species, or that the study site is too small, meaning the anteaters interact more often. In addition, proximity analysis highlights that low home-range overlap cannot be strongly interpreted as a lack of individual interaction. Proximity events could indicate reproductive behaviour.

However, we still do not know if there is reproductive seasonality for the species, and this needs further study to advance our knowledge of this species’ natural history. Despite giant anteaters being most well-studied anteater species, we still lack the basic knowledge to to ask the right questions. We need to apply much more effort to studies on human-modified areas, to reach the minimal information needed to understand population trends and to move conservation forward.

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