Abstract
Studying the variables that describe the spatial ecology of threatened species allows us to identify and prioritize areas that are critical for species conservation. To estimate the home range and core area of the Endangered (EN) Amazon river dolphinInia geoffrensis, 23 individuals (6♀, 17♂) were tagged during the rising water period in the Amazon and Orinoco river basins between 2017 and 2018. The satellite tracking period ranged from 24 to 336 d (mean ± SE = 107 ± 15.7 d), and river dolphin movements ranged from 7.5 to 298 km (58 ± 13.4 km). Kernel density estimates were used to determine minimum home ranges at 95% (K95= 6.2 to 233.9 km2; mean = 59 ± 13.5 km2) and core areas at 50% (K50= 0.6 to 54.9 km2; mean = 9 ± 2.6 km2). Protected areas accounted for 45% of the K50estimated core area. We observed dolphin individuals crossing country borders between Colombia and Peru in the Amazon basin, and between Colombia and Venezuela in the Orinoco basin. Satellite tracking allowed us to determine the different uses of riverine habitat types: main rivers (channels and bays, 52% of recorded locations), confluences (32%), lagoons (9.6%), and tributaries (6.2%). Satellite monitoring allowed us to better understand the ecological preferences of the species and demonstrated the importance of maintaining aquatic landscape heterogeneity and spatial connectivity for effective river dolphin conservation.
Highlights
The home range of animals is an important spatial ecological variable operating as a proxy for a species’ biological needs (Kenward 2001, Hemson et al 2005), and its key resource supply (Flores & Bazzalo 2004)
Ecological and threat variables considered here included: (1) biogeographic influence and water types, i.e. black, clear, white, and mixed (Sioli 1984, Junk & Furch 1993, Hoorn & Wesselingh 2010); (2) habitat types, i.e. main rivers with várzea, confluences, tributaries, and lagoons with igapó (Amazon forests flooded by blackwaters) (Trujillo 2000, Martin & da Silva 2004b, Gómez-Salazar et al 2012c); (3) proximity to protected areas, i.e. national and regional natural parks, reserves, and Ramsar sites; and (4) threats to river dolphin populations, i.e. gold mining, dams, and by-catch (Table 1)
Our results indicate that Amazon river dolphins use a diverse range of aquatic ecosystems in at least 7 protected areas in 4 countries
Summary
The home range of animals is an important spatial ecological variable operating as a proxy for a species’ biological needs (Kenward 2001, Hemson et al 2005), and its key resource supply (Flores & Bazzalo 2004). The home range of some cetacean species is related to (1) animal body mass (Harestad & Bunnel 1979, Swihart et al 1988, Gubbins 2002); (2) sex and age (Wells 1991); (3) the density of conspecifics; and (4) the distribution of mates (Ostfeld 1990). Home ranges are good predictors of productivity and habitat heterogeneity, enabling ecological comparisons among geographically distinct populations (Ballance 1992, Gubbins 2002, Ouellette & Cardille 2011). Kernel density estimators are useful for quantifying the intensity of habitat use (Worton 1989, Ouellette & Cardille 2011) and are among the most robust and widely applied non-parametric statistical methods for estimating the probability of the occurrence of individuals (Seaman & Powell 1996, Seaman et al 1999, Powell 2000, Oshima et al 2010)
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