Modelling the abundance and productivity distribution to understand the habitat–species relationship: the guanaco (Lama guanicoe) case study

Abstract

ContextThe conservation of large wild herbivores presents a challenge posed by the fact that their broad habitat requirements overlap with various human activities. Elucidating the factors that explain their distribution patterns provides us with a better understanding of habitat–species relationships and facilitates the design of effective management policies. AimsIdentify the natural (forage availability, weather) and anthropogenic (hunting, interspecific competition) factors that explain the abundance and productivity distribution of the guanaco. Estimate guanaco abundance and productivity and describe their distribution. MethodsWe estimated the abundance and productivity of guanaco by using aerial surveys during the breeding and non-breeding season of two consecutive years, following the strip-transect methodology; we then modelled these as a function of environmental factors by means of density surface models. Key resultsThe highest abundance and productivity of guanaco occurred mostly where mesic grassland was dominant. Guanaco abundance presented three hotspots on the basis of geographic location, and family groups were more productive at low to intermediate livestock level. Abundance was significantly higher in the breeding season for both years (5614 and 14092 individuals) than in the non-breeding season (2922 and 6926 individuals), and it was higher in 2015 than in 2014. Productivity was higher in 2015 than in 2014 (0.54 and 0.46 calves per adult respectively). ConclusionsGuanaco responded to forage availability, occupying zones with low to intermediate food availability in the breeding season, and those with the highest availability in the non-breeding season. This could be due to interspecific competition between livestock and guanaco family groups. We propose that the overall guanaco response could also be explained by social structure or by unassessed factors such as predation risk by feral dogs. ImplicationsThe guanaco could compensate for the use of habitats with a lower food availability during the breeding season by using better-quality habitats during the non-breeding season.

Human–wildlife conflicts in Patagonia: ranchers’ perceptions of guanacoLama guanicoeabundance

“…We estimated actual guanaco abundance with density surface modelling (Miller et al, 2013), used in previous studies of guanaco abundance (Flores et al, 2018, 2020). This approach links recorded individuals and covariates through a spatially explicit model to explain variability in abundance as well as to make predictions regarding abundance in unsampled areas (Miller et al, 2013).…”

“…Transects were 1,400 m wide (700 m each side of the flight trajectory), as previously used by Flores et al (2018, 2020). The detection probability of guanacos on the transect was assumed to be constant and equal to 1.…”

Competitive exclusion and herbivore management in a context of livestock‐wildlife conflict

“…2017; Antún & Baldi 2020; Flores et al . 2020), with guanacos often restricted to poorer habitat or livestock‐free areas, such as wildlife reserves. However, in recent years, the increase in guanaco densities within certain ranches, along with the historical overgrazing issues affecting Patagonian rangelands, has exacerbated the conflict and the need of scientific verification of the assumptions underlying current management initiatives has become evident.…”

“…Since some of their populations started to recover, management decisions are increasingly driven by political pressure exerted by the livestock industry who perceive guanacos as responsible for lowered livestock production or degraded land, arguing that guanacos outcompete sheep for forage resources and that their numbers are out of control. Although these affirmations are based on perceptions rather than scientific evidence, numerous publications have reported a negative relationship between guanaco and livestock densities at landscape scale (Raedeke 1979;Baldi et al 2001;Pedrana et al 2010;Nabte et al 2013;Schroeder et al 2014;Moraga et al 2015;Rivas et al 2015;Traba et al 2017;Ant un & Baldi 2020;Flores et al 2020), with guanacos often restricted to poorer habitat or livestock-free areas, such as wildlife reserves. However, in recent years, the increase in guanaco densities within certain ranches, along with the historical overgrazing issues affecting Patagonian rangelands, has exacerbated the conflict and the need of scientific verification of the assumptions underlying current management initiatives has become evident.…”