INVESTIGADORES
ZANON MARTINEZ Juan Ignacio
congresos y reuniones científicas
Título:
Feral donkey (Equus assinus) and guanaco (Lama guanicoe) abundances and group characteristics before and after donkey removal in northwestern Argentina
Autor/es:
R. CREGO; E. DONADIO; M. VITALI; M. RUIZ BLANCO; JUAN IGNACIO ZANÓN MARTÍNEZ; V. SALVADOR; M.J. VEINTICINCO; J. GUIDO; F.N. MOSCHIONE
Reunión:
Congreso; 10th International Mammal Congress; 2009
Resumen:
Introduced species could negatively influence the abundance and distribution of native species. Currently, feral donkey Equs assinus populations inhabit northwestern Argentina even inside protected areas. In 2007, 517 feral donkeys were removed from Los Cardones National Park, Salta province, Argentina. We aimed to (1) quantitatively evaluate the effect of such removal on the abundance of donkeys and a native ungulate species, the guanaco Lama guanicoe; (2) analyze modifications in donkey and guanaco group size; and (3) investigate changes in age structure (number of juveniles divided the total number of individuals observed×100) for populations of both species. We conducted fieldwork in July 2006 (pre-removal) and August 2 08 (post-removal). We estimated donkey and guanaco abundances using the line transect method and program DISTANCE 5.0. Mean abundances [95% CI; CV] of donkeys (2006: 0.82 ind/km2 [0.17-3.95; 59.3%]; 2008: 0.39 [0.10-1.56; 50.9%]) and guanacos (2006: 1.03 [0.12-8.67; 78%]; 2008: 0.52 [0.14-1.92; 50.1%]) decreased by 50% after removal. These differences were marginally significant for donkeys (p=0.08; t=1.639) and non-significant for guanacos (p=0.13; t=1.208). We did not detect between-year changes in group size (mean [95% CI]) neither in donkeys (2006: 3.9 individuals [2.6-5.1]; 2008: 3.3 [2.4-4.2]) or guanacos (2006: 8.0 [6.2-9.8]; 2008: 6.7 [4.2-9.2]). We observed a sharp increment in the prevalence of juvenile donkeys within the donkey population (2006: 0.8% [0-3.7]; 2008: 5.8 [2.8-9.9]) and a modest increment in the prevalence of juvenile guanacos (2006: 6.7% [3.6-10]; 2008: 8.9 [4.4-13.1]). Our data suggest that donkey removal effectively decreased donkey abundance; however, it appears to have also enhanced the reproductive success of donkeys likely via decreasing intra-specific competition. The lack of response observed in the guanaco population may be explained by the short period of time passed since donkey removal.