The squirrel monkey, Saimiri, is a pan-Amazonian Pleistocene radiation. We use statistical phylogeographic methods to create a mitochondrial DNA-based timetree for 118 squirrel monkey samples across 68 localities spanning all Amazonian centers of endemism, with the aim of better understanding (1) the effects of rivers as barriers to dispersal and distribution; (2) the area of origin for modern Saimiri; (3) whether ancestral Saimiri was a lowland lake-affiliated or an upland forest taxa; and (4) the effects of Pleistocene climate fluctuation on speciation. We also use our topology to help resolve current controversies in Saimiri taxonomy and species relationships. The Rondônia and Inambari centers in the southern Amazon were recovered as the most likely areas of origin for Saimiri. The Amazon River proved a strong barrier to dispersal, and squirrel monkey expansion and diversification was rapid, with all speciation events estimated to occur between 1.4 and 0.6Ma, predating the last three glacial maxima and eliminating climate extremes as the main driver of squirrel monkey speciation. Saimiri expansion was concentrated first in central and western Amazonia, which according to the "Young Amazon" hypothesis was just becoming available as floodplain habitat with the draining of the Amazon Lake. Squirrel monkeys also expanded and diversified east, both north and south of the Amazon, coincident with the formation of new rivers. This evolutionary history is most consistent with a Young Amazon Flooded Forest Taxa model, suggesting Saimiri has always maintained a lowland wetlands niche and was able to greatly expand its range with the transition from a lacustrine to a riverine system in Amazonia. Saimiri vanzolinii was recovered as the sister group to one clade of Saimiri ustus, discordant with the traditional Gothic vs. Roman morphological division of squirrel monkeys. We also found paraphyly within each of the currently recognized species: S. sciureus, S. ustus, and S. macrodon. We discuss evidence for taxonomic revision within the genus Saimiri, and the need for future work using nuclear markers.
4 Programa de P os-Graduac ßão em Recursos Naturais da Amazônia, Universidade Federal do Oeste do Par a, Santar em, Par a, Brazil Correspondence Rafael M. Rabelo, Programa de P os-Graduac ßão em Ecologia,
AbstractAim: We tested the "habitat amount hypothesis", which predicts that the effect of patch size on number of species results from a "sample area effect" rather than an "island effect". Specifically, we (1) compared parameters of the species-area relationship (SAR) of arboreal mammals in forested fluvial islands and continuous forest, and (2) separated the effects of island size and of landscape-scale habitat amount on species richness.Location: Middle-Solimões River region, Central Amazon.
Methods:We surveyed arboreal mammals along line-transects on 15 fluvial floodplain islands and nine transects in continuous floodplain forest. Transect length varied according to island size. Transects of similar length were established in continuous forest. We used power transformed (log-log) models to construct a SAR for the set of island transects and another SAR for the set of continuous forest transects. We compared slope and intercept between the two SARs using ANCOVA. We used multiple regressions to separate the effects of island size and of habitat amount on the rarefied number of species across multiple spatial scales (500-6,000 m).
Results:The two species-area curves showed similar slopes, but the intercept was lower for islands. Multiple regressions showed the best fit at the 5,500 m spatial scale.At this scale, habitat amount predicted species richness, whereas island size did not.
Main conclusions:We conclude that the apparent effect of patch size on the number of species may be simply due to the sample area effect and that no island effect operates on this patchy system. Accordingly, island size per se does not increase the number of species at a sample site. Fluvial islands should not be treated as "real" islands from the island biogeography perspective. In sum, we found support for the habitat amount hypothesis for predicting the richness of arboreal mammals on fluvial islands.
K E Y W O R D SAmazon, fluvial landscapes, habitat amount hypothesis, island biogeography, island effect, local patch, river dynamics, sample area effect, species richness, species-area curve
The rate of deforestation in the Amazon is increasing. Predictive models estimate that as a result of agricultural expansion 40% of these forests will be lost by 2050. As a consequence the habitat of forest-dwelling species such as the Endangered black-faced black spider monkey Ateles chamek is being lost, particularly along the arc of deforestation in the Brazilian Amazon. We used species distribution modelling to (1) define the distribution of this spider monkey, using environmental predictors, (2) calculate the area of this distribution covered by the protected area network, and (3) calculate the expected loss of the species’ habitat under future scenarios of deforestation. We found that the species occupies only c. 28% of its extent of occurrence. Only 32% of the species’ area of occupancy is legally protected, and the modelling suggests that 31–40% of the species’ habitat will be lost by 2050. We highlight three unprotected regions with extensive forest cover that are predicted to become severely deforested by 2050 as priority regions for expanding the protected area network. We also propose landscape management and restoration in three human-modified regions. Our study provides an example of how species distribution modelling can be applied to assess threats to species and support decision makers in implementing conservation actions.
Nested structures of species assemblages have been frequently associated with patch size and isolation, leading to the conclusion that colonization–extinction dynamics drives nestedness. The ‘passive sampling’ model states that the regional abundance of species randomly determines their occurrence in patches. The ‘habitat amount hypothesis’ also challenges patch size and isolation effects, arguing that they occur because of a ‘sample area effect’. Here, we (a) ask whether the structure of the mammal assemblages of fluvial islands shows a nested pattern, (b) test whether species’ regional abundance predicts species’ occurrence on islands, and (c) ask whether habitat amount in the landscape and matrix resistance to biological flow predict the islands’ species composition. We quantified nestedness and tested its significance using null models. We used a regression model to analyze whether a species’ relative regional abundance predicts its incidence on islands. We accessed islands’ species composition by an NMDS ordination and used multiple regression to evaluate how species composition responds to habitat amount and matrix resistance. The degree of nestedness did not differ from that expected by the passive sampling hypothesis. Likewise, species’ regional abundance predicted its occurrence on islands. Habitat amount successfully predicted the species composition on islands, whereas matrix resistance did not. We suggest the application of habitat amount hypothesis for predicting species composition in other patchy systems. Although the island biogeography perspective has dominated the literature, we suggest that the passive sampling perspective is more appropriate for explaining the assemblages’ structure in this and other non‐equilibrium patch systems.
Abstract in Portuguese is available with online material.
Descriptions of new tool-use events are important for understanding how ecological context may drive the evolution of tool use among primate traditions. Here, we report a possible case of the first record of tool use by wild Amazonian capuchin monkeys (Sapajus macrocephalus). The record was made by a camera trap, while we were monitoring caiman nest predation at Mamirauá Reserve in Central Amazonia. An adult individual was registered in a bipedal posture, apparently using a branch as a shovel to dig eggs out of a nest. Caiman eggs are frequently depredated by opportunistic animals, such as the capuchin monkeys. As the Mamirauá Reserve is covered by a high-productivity forest, and caiman eggs are a high-quality food resource seasonally available on the ground, we believe that tool use by capuchins is more likely to be opportunity driven, rather than necessity driven, in our study site.
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