conservation.arizona.edu - peripheral population

Altered natal dispersal at the range periphery: the role of behavior, resources, and maternal condition.

thackerk1 — Tue, 23 Jul 2019 23:22:46 +0000

Authors

Melissa J. Merrick

John L. Koprowski

Natal dispersal outcomes are an interplay between environmental conditions and individual phenotypes. Peripheral, isolated populations may experience altered environmental conditions and natal dispersal patterns that differ from populations in contiguous landscapes. We document nonphilopatric, sex-biased natal dispersal in an endangered small mammal, the Mt. Graham red squirrel (Tamiasciurus hudsonicus grahamensis), restricted to a single mountain. Other North American red squirrel populations are shown to have sex-unbiased, philopatric natal dispersal. We ask what environmental and intrinsic factors may be driving this atypical natal dispersal pat- tern. We test for the influence of proximate factors and ultimate drivers of natal dispersal: habitat fragmentation, local population density, individual behavior traits, inbreeding avoidance, competition for mates, and competition for resources, allow- ing us to better understand altered natal dispersal patterns at the periphery of a species’ range. A juvenile squirrel’s body condition and its mother’s mass in spring (a reflection of her intrinsic quality and territory quality) contribute to individual behavioral tendencies for movement and exploration. Resources, behavior, and body condition have the strongest influence on natal dispersal distance, but affect males and females differently. Male natal dispersal distance is positively influenced by its moth- er’s spring body mass and individual tendency for movement; female natal dispersal distance is negatively influenced by its mother’s spring body mass and positively influenced by individual tendency for movement. An apparent feedback between environmental variables and subsequent juvenile behavioral state contributes to an altered natal dispersal pattern in a peripheral population, highlighting the importance of studying ecological processes at the both range center and periphery of species’ distributions.

Additional Information

Ecology and Evolution

Date of publication:

2016

Topics

Mount Graham Red Squirrel

behavioral phenotype maternal effects

peripheral population

condition-dependent dispersal

phenotype-dependent dispersal

Research Categories

Behavioral Ecology Population Ecology Sky Islands Spatial Ecology Threatened and Endangered Species

Functional semelparity drives population dynamics and endangers a peripheral population

thackerk1 — Thu, 27 Jun 2019 22:38:23 +0000

Authors

Emily A. Goldstein

Melissa J. Merrick

John L. Koprowski

Despite increased risk of extinction through stochastic events, peripheral populations are conservation priorities as the distribution of endangered species tends to contract to the periphery of historic ranges rather than toward the core. Trailing-edge populations and mountain isolates, which may become more common as climate change drives range shifts, are an important realm of inquiry and contain important reserves of genetic variation. We use long-term monitoring data from the southernmost population of a widespread species to test the hypothesis that peripheral populations display distinct demographic profiles from core populations. The red squirrel (Tamiasciurus hudsonicus) is predicted to recede from its southern border in response to climate-induced habitat change. We estimate key demographic parameters for this endangered population using survival and reproduction schedules and compare the dynamics to core populations of this and related species. This peripheral population exhibits higher adult mortality, and suffers associated impacts on reproductive output, which results in a demography distinct from core populations and phylogenetically similar species. Poor adult survival, similar to a population that experiences extremely high hunting pressure, has resulted in this normally iteroparous species becoming functionally semelparous at the periphery. Understanding differences in demographic function between peripheral and core populations is key if management strategies are to be effective in supporting continued persistence of at risk populations in the face of range shifts of species or habitats driven by environmental change.

Additional Information

Biological Conservation 205:52-59.

Date of publication:

2016

Topics

sky island

red squirrel

life table

trailing edge

peripheral population

Research Categories

Natural History Population Ecology Sky Islands Threatened and Endangered Species

Low survival, high predation pressure present conservation challenges for an endangered endemic forest mammal

thackerk1 — Thu, 27 Jun 2019 22:19:15 +0000

Authors

Emily A. Goldstein

Melissa J. Merrick

John L. Koprowski

Knowledge of which population parameters and mortality risks contribute most to population decline and endangerment is necessary to develop informed and actionable conservation plans for threatened and endangered species (Rushton et al., 2006). The federally endangered Mount Graham red squirrel (Tamiasciurus fremonti grahamensis) is restricted to the Pinaleño Mountains, in southeastern Arizona, USA. The population is critically threatened with extensive habitat loss from fire as well as by an introduced non-native squirrel species, the Abert's squirrel (Sciurus aberti). Recovery is challenged by low survival and poor reproduction, such that the subspecies is functionally semelparous. We calculate survival rates and cause-specific mortality hazards from known-fate individuals to understand the impact of predation on survival and demography in this peripheral population. We document the lowest survival and highest rates of mortality in any population of North American red squirrels in both adult and juvenile age classes (mean annual survival: adults = 0.32, juveniles = 0.26). We attributed the majority of confirmed deaths to avian predation (adults 65%, juveniles 75%), and the daily hazard rate for avian predation was 15 times higher than for mammalian predation and 2 times higher than death from unknown causes. It is likely that the presence of an ecologically similar, non-native tree squirrel subsidizes a diverse avian predator guild, which includes two raptor species of conservation concern. In addition to efforts to remove the non-native Abert's squirrel, we recommend immediate forest restoration efforts in the long term, and habitat augmentation to increase structural complexity, cover, shelter, and food resources in the short term.

Additional Information

Biological Conservation

Date of publication:

2018

Topics

cause-specific morality

Mount Graham Red Squirrel

Abert’s squirrels

apparent competition

peripheral population

Research Categories

Population Ecology Sky Islands Threatened and Endangered Species