Status of the Slender Mouse-ear-cress (Halimolobos virgata or Transberingia bursifolia susp. virgata) in Alberta : update 2009 /

Every five years, the Fish and Wildlife Division of Alberta Sustainable Resource Development reviews the general status of wildlife species in Alberta.These overviews, which have been conducted in 1991 ( The Status of Alberta Wildlife ), 1996 ( The Status of Alberta Wildlife ), 2000 (The General Status of Alberta Wild Species 2000), and 2005 (The General Status of Alberta Wild Species 2005 ) assign individual species "ranks" that reflect the perceived level of risk to populations that occur in the province.Such designations are determined from extensive consultations with professional and amateur biologists, and from a variety of readily available sources of population data.A key objective of these reviews is to identify species that may be considered for more detailed status determinations.The Alberta Wildlife Status Report Series is an extension of the general status exercise, and provides comprehensive current summaries of the biological status of selected wildlife species in Alberta.Priority is given to species that are At Risk or May Be At Risk in the province, that are of uncertain status (Undetermined), or that are considered to be at risk at a national level by the Committee on the Status of Endangered Wildlife in Canada (COSEWIC).Reports in this series are published and distributed by the Alberta Conservation Association and the Fish and Wildlife Division of Alberta Sustainable Resource Development.They are intended to provide detailed and up-to-date information that will be useful to resource professionals for managing populations of species and their habitats in the province.The reports are also designed to provide current information that will assist Alberta's Endangered Species Conservation Committee in identifying species that may be formally designated as Endangered or Threatened under Alberta's Wildlife Act.To achieve these goals, the reports have been authored and/or reviewed by individuals with unique local expertise in the biology and management of each species.iii EXECUTIVE SUMMARY Slender mouse-ear-cress ( Halimolobos virgata or Transberingia bursifolia subsp.virgata) is an herbaceous plant distributed in the mixedgrass prairie on the plains of southeast Alberta and southwest Saskatchewan, and across semi-arid mountain ranges and intervening basins and plateaux of seven western states.It is listed as Threatened federally and also provincially by the Saskatchewan government.In Alberta, evaluation of a 2005 provincial status report resulted in a recommended status of Data Deficient by the Alberta Endangered Species Conservation Committee and its Scientific Subcommittee.Results of additional surveys in known and potential habitat for slender mouse-ear-cress are incorporated into this updated status report to assist in the evaluation of its provincial status.Suitable habitat for slender mouse-ear-cress in Alberta is characterized as undulating to rolling native grassland on silty to sandy deposits of fluvial or eolian origin.It may be associated with ephemerally wet depressions and drainages.Fourteen subpopulations are recognized in Alberta: one is ranked as extirpated, one as historical, three as failed-to-find during subsequent surveys and nine as extant.Substantial rare plant search effort over the last few decades, and particularly within the last few years, in apparently suitable habitat has resulted in reports of only a few additional subpopulations of slender mouse-ear-cress.The extent of occurrence of all subpopulations in Alberta is about 9998 km2; that of only extant ones is about 530 km2.Considering only extant subpopulations, the area occupied by slender mouse-ear-cress is estimated to be 18 km2 (the sum of occupied 1-km x 1-km squares).This number could be less than 0.05 km2, based on the number and maximum size of unique locations in the Alberta Natural Heritage Information Centre database.The provincial population of slender mouse-ear-cress is estimated to be in the order of several thousand (3000-7000) reproducing individuals in years when conditions are suitable for germination and growth.Data over multiple years at some sites indicate large fluctuations in number of reproducing individuals, depending on environmental conditions such as timing and amount of rainfall in spring.Alberta's extant population of slender mouse-ear-cress is approximately 45 km from the closest known subpopulation in Saskatchewan and 200 km from the nearest subpopulation in the Sweetgrass Hills of Montana.The next nearest known populations are about 450 km south in the Tendoy Mountains of southwest Montana and in the Absaroka Range of northwest Wyoming.Loss of native grasslands within the range of slender mouse-ear-cress is affecting habitat quality and availability.Native prairie decline is caused primarily by agriculture expansion, urban development, oil and gas development and the construction of transportation and utility corridors, as well as the spread of invasive non-native species in fragmented landscapes.Since 1970, bare ground resulting from agriculture (cultivation) and industrial development has increased 40% and linear disturbance has increased 93% in a regional study area that encompasses all of the range of extant slender mouse-ear-cress subpopulations.The trend in loss of native grasslands is expected to continue.Other potential limiting factors for slender mouse-ear-cress are climate change and altered fire and grazing regimes beyond the range of natural variation.A draft recovery strategy for slender mouse-ear-cress in Canada has recently been developed by Environment Canada.

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