Demographic consequences of age-structure in extreme environments: population models for arctic and alpine ptarmigan

Abstract

Organisms living in arctic and alpine environments are increasingly impacted by human activities. To evaluate the potential impacts of global change, a better understanding of the demography of organisms in extreme environments is needed. In this study, we compare the age-specific demography of willow ptarmigan (Lagopus lagopus) breeding at arctic and subalpine sites, and white-tailed ptarmigan (L. leucurus) breeding at an alpine site. Rates of egg production improved with age at the alpine and subalpine sites, but the stochastic effects of nest and brood predation led to similar rates of annual fecundity among 1-, 2-, and 3+-year-old females. All populations had short generation times (T<2.7 years) and low net reproductive rates (R0<1.2). Stable age distributions were weighted towards 1-year-old females in willow ptarmigan (>59%), and to 3+-year-old females in white-tailed ptarmigan (>47%). High damping ratios (rho>3.2) indicated that asymptotic estimates were likely to match natural age distributions. Sensitivity and elasticity values indicated that changes in juvenile survival would have the greatest impact on the finite rate of population change (lambda) in willow ptarmigan, whereas changes to the survival of 3+-year-old females would have a greater effect in white-tailed ptarmigan. High survivorship buffers white-tailed ptarmigan in alpine environments against the potential effects of climate change on annual fecundity, but may make the species more sensitive to the effects of pollutants or harvesting on adult survival. Conversely, processes that reduce annual fecundity would have a greater impact on the population viability of willow ptarmigan in arctic and subalpine environments. If these same demographic patterns prove to be widespread among organisms in extreme environments, it may be possible to develop general recommendations for conservation of the biological resources of arctic and alpine ecosystems.

Nesting success and productivity of Tucuman Parrots(Amazona tucumana)in high-altitude forests of Argentina: do they differ from lowlandAmazonaparrots?

“…These results differ from trends observed in other bird species that tend to shift to a slower life-history strategy with increased elevation (Sandercock et al 2005a(Sandercock et al , 2005b. There are several alternative explanations for our finding that the Tucuman Parrot has the second largest clutch-size among Amazona parrots.…”

Ptarmigan in North America: Influence of Life History and Environmental Conditions on Population Persistence.

“…Vital rates at later life history stages are predicted to have relatively less influence than survival or fecundity of younger birds. Adapted after data in Sandercock et al (2005b).…”

“…From this, Sandercock et al (2005b) calculated an elasticity measure (which is the change predicted in the population growth rate from a proportional change in a vital rate) for our populations of Willow Ptarmigan in Churchill, Manitoba and in British Columbia to reveal which vital rate is the most influential. By far the most important vital rate in predicting future population growth for both populations was the survival of juveniles from fledging to the following breeding season.…”

“…By far the most important vital rate in predicting future population growth for both populations was the survival of juveniles from fledging to the following breeding season. The second most important variable was the fecundity of yearling birds (Sandercock et al 2005b). This means that Willow Ptarmigan in much of their range, likely including both Europe and North America, have a fast life history that is characterized by high fecundity (1.33-2.04 female young/hen), relatively low annual adult survival (37-43%), and short generation times (Sandercock et al 2005a,b, Hannon and Martin 2006, Hannon et al 1998).…”

Large-scale climate variability and rodent abundance modulates recruitment rates in Willow Ptarmigan (Lagopus lagopus)

“…The Willow Ptarmigan (Lagopus lagopus) is a medium-sized grouse distributed in alpine tundra habitats in the northern hemisphere (Johnsgard 1983). They have a short generation time (T = 1.8, Sandercock et al 2005 andannual mortality[46 %, Sandercock et al 2011;Smith and Willebrand 1999) and each female may produce up to 12 chicks annually, although recruitment of juveniles as well as densities of breeding birds vary both in time and space (Johnsgard 1983;Kvasnes et al 2013). Several studies have documented that weather conditions during the breeding season can influence recruitment rates in ptarmigan (Hannon and Martin 2006;Novoa et al 2008;Slagsvold 1975;Martin and Wiebe 2004;Steen et al 1988a, b).…”