Forest Investment Account (FIA) - Forest Science Program
FIA Project Y091082

    Conservation genetics and ecology of the threatened Coastal Giant Salamander in managed forests of British Columbia: setting priorities for an integrative species recovery plan
 
Project lead: Richardson, John (University of British Columbia)
Subject: Forest Investment Account (FIA), British Columbia
Series: Forest Investment Account (FIA) - Forest Science Program
Description:
The Coastal Giant Salamander (CGS) (Dicamptodon tenebrosus) is a highly vulnerable amphibian that only occurs on the west coast of North America. In Canada, CGS is on the provincial Red List in British Columbia (BC) and is designated as Threatened in Canada (COSEWIC 2002), in addition to being one of BC’s ‘Identified Wildlife’. CGS is restricted to approximately 60 streams within a single watershed in Canada, occurring in less than 100 km² in the Chilliwack River Valley of BC. This species is highly susceptible to habitat loss and degradation due to encroaching development, logging and road building. Logging reduces CGS habitat quality by disturbing stream and bank geomorphology, reducing canopy cover, and altering prey assemblages. There is a distinct possibility that CGS could go extinct in Canada as a direct result of forestry activities. The continued survival of this fragile species therefore depends primarily on ecologically sensitive forestry practices.

Previous research has shown that CGS may suffer from reduced larval density, restricted movement and lower genetic variation in clear-cut sites compared with forested sites [1, 2]. This signifies the disruption of important population processes that can alter the dispersal ability, mating system and social organisation of CGS populations. The likely consequences are elevated genetic relatedness and subsequent inbreeding depression, leading to population declines and an increased risk of extinction. Although these threats are recognized in a general sense, their specific effects on population processes remain largely unknown, and hence there are inadequate data to devise strategies to avoid or mitigate the threats.

Current forest management policies provide limited protection for CGS habitat. Although vegetation buffer strips are retained along fish-bearing streams these measures do not protect threatened CGS populations because they rarely occur in streams containing fish. Habitat protection through the establishment of forested buffer strips and Wildlife Habitat Areas along small headwater streams is considered most important for CGS recovery. However, the effectiveness of WHAs and buffer strips for maintaining natural population dynamics and processes in CGS remains unexamined. A small number of sites with buffer strips containing CGS exist, while 18 Wildlife Habitat Areas have been approved under the CGS recovery strategy, enabling this core management option to be assessed.

There have been some studies on the limited dispersal ability of CGS larvae and terrestrial adults, with evidence for restricted movement in clear-cut sites [3, 4, 5], but little is known about age and sex specific dispersal and long distance movements over extended time periods in both aquatic and terrestrial habitats. This information is critical to identify, maintain, or restore a connected network of terrestrial and aquatic dispersal habitats for CGS. Knowledge of the long-term effects of forestry practices and the mitigating effects of buffer zones on CGS dispersal pathways is needed to prioritise habitat conservation measures.
Obtaining information on salamander dispersal distance and reproductive behaviour is difficult or impossible using standard ecological tools, but with the advent of highly variable molecular markers such questions can be efficiently addressed. Although reduced genetic variation has been found in CGS within clear-cut sites compared with second and old-growth sites [2], the consequences of this for population dynamics at finer geographical scales is unstudied. By altering patterns of dispersal, habitat alteration and fragmentation through forest harvesting has the potential to disrupt the social organisation and mating system of CGS. Such habitat changes can lead to an increased chance of mating among relatives and elevated levels of inbreeding, resulting in population declines and increased risk of extinction.

We aim to investigate the impact of forestry practices on vital population processes in CGS within the Chilliwack River Valley, using a powerful combination of molecular ecological and demographic studies. Our specific aims can be divided into four main parts:
1) We will use genetic markers and mark-recapture data to investigate population sizes, dispersal and gene flow of larvae, juveniles and adults within and across five replicated forest treatments: (1) clear-cut sites (3-9 years); (2) clear-cut sites with buffer strips (3-9 years); (3) second growth forest (30-60 years); (4) WHAs; and (5) old growth forest (> 250 years) (control site). This will reveal the metapopulation dynamics (e.g. migration rates and connectivity) of CGS populations across and within streams, enabling the susceptibility of populations to demographic and/or environmental stochasticity to be assessed. The occurrence of recent population bottlenecks (i.e. loss of genetic diversity due to rapid population decline) will also be examined across treatments.
2) Aspects of the socioecology (genetic relatedness, mating system, age and sex-biased dispersal) of CGS will be compared across forest treatments to examine the influence of management practices on fine-scale population processes. Genetically determined family relationships will be examined among individuals within and across sampling localities, elucidating aspects of CGS reproductive behaviour through sib-ship reconstruction analyses (e.g. evidence for polygamy or polyandry). Genetic analyses will also enable migrants to be identified and allow the incidence of inbreeding avoidance mechanisms to be examined (i.e. through mate-choice or sex-biased dispersal). Patterns occurring in undisturbed old growth forests will provide a control from which comparisons across sites can be made.
3) We will investigate how the spatial organisation of CGS within forest treatments varies with habitat quality, allowing population densities to be ascertained over fine spatial scales across harvested and old growth sites. Biological and physical habitat features will be recorded at all collection sites, including water quality, stream characteristics and terrestrial features. In conjunction with genetic insights and inter-annual growth measurements (from mark-recapture), habitat quality and suitability for CGS will be evaluated across forest treatments to establish relationships with CGS density and distribution.
4) It is not known whether Canadian and US populations of CGS are genetically distinct, and are therefore undergoing distinct evolutionary processes. This is particularly notable as Canadian CGS populations are at the absolute periphery of their global range, which extends south into California. Microsatellite markers will be used to examine genetic divergence between Canadian CGS populations and their potential source populations in the United States. Such information is necessary to define evolutionary significant units, whereby the aim is to maintain the evolutionary potential of species in conjunction with sustainable population sizes. This is of particular value in the event that CGS is faced with high extinction risk, as we will assess whether translocation of CGS from high density US populations into Canada is a viable and safe option for restoring genetic variation.

The primary objective of this project is to assess the capacity of WHAs and streams with buffer strips to retain ecological patterns found within unharvested sites, incorporating the effects of landscape features (e.g. natural barriers to gene-flow), forestry-related infrastructure (e.g. roads, dams), and urban development activities on population processes. The size and dimensions of WHAs and the width of buffer zones will also be factored into the analyses. The project outcomes will be used to evaluate the effectiveness of WHAs and provide options for optimising their size and structure, so that natural population dynamics and dispersal patterns of CGS can be maintained or restored.
Related projects:  FSP_Y102082FSP_Y113082
Contact: Richardson, John, (604) 822-6586, john.richardson@ubc.ca

    Deliverables:

Executive summary (0.1Mb)

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Updated May 02, 2011 

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