Species

BackWalckenaeria grandis (Wunderlich, 1992)

Walckenaeria grandis (Wunderlich, 1992)

  • Kingdom: Animalia
  • Phylum: Arthropoda
  • Class: Arachnida
  • Order: Araneae
  • Family: Linyphiidae
VU Vulnerable
IUCN Red List Status:

Countries of Occurrence:
Portugal - Azores

Archipelago(s):
Azores

Reviewer/s:
Russell, N.

Contributor/s:
Mendonca, E. & Lamelas-López, L.

Facilitators / Compilers/s:


Assessment Rationale:

Walckenaeria grandis is an Azorean endemic species, occurring in Flores, Pico, São Jorge, Terceira and S. Miguel islands (Azores, Portugal) (Borges et al. 2010). It is a relatively rare species, with a large Extent of Occurrence (ca. 18,436-19,600 km2 ) and a relatively small Area of Occupancy (AOO) (88-172 km²). There is a continuing decline in the AOO, extent and quality of habitat as well as the number of mature individuals as a result of the invasions of non-native plants and trampling of soil by dairy cows. The species is only relatively abundant at high elevation pristine native forests and grasslands. In the past, the species has probably strongly declined due to changes in habitat size. The species is assessed as Vulnerable (VU). We suggest as future measures of conservation: (1) a long-term monitoring plan of the species; (2) control of invasive species, and (3) restriction of the access of cattle to areas of native habitat.

Geographic Range:

Walckenaeria grandis is an Azorean endemic species occurring in Flores, Pico, São Jorge, Terceira and S. Miguel islands (Azores, Portugal) (Borges et al. 2010), known from ten Natural Forest Reserves: Caldeiras Funda e Rasa and Morro Alto e Pico da Sé (Natural Park of Flores); Caveiro and Caiado (Natural Park of Pico); Topo (Natural Park of S. Jorge); Biscoito da Ferraria, Pico Galhardo, Caldeira Sta. Bárbara e Mistérios Negros and Terra Brava (Natural Park of Terceira); Graminhais (Natural Park of S. Miguel). The Extent of Occurrence (EOO) is ca. 18,436-19,600 km2 and the Area of Occupancy (AOO) is 88-172 km2 .

Regions:
Portugal - Azores
Extent of Occurrence (EOO):
18,436-19,600 (km2)
Area of Occupancy (AOO):
88-172 (km2)
Elevation Lower Limit:
(m)
Elevation Upper Limit:
(m)
Biogeographic Realms:
Palearctic
Presence:
Extant
Origin:
Endemic Azores
Seasonality:
Resident

Population:

This is a relatively rare species that is abundant only at high elevation in very pristine sites. A continuing decline in the number of mature individuals is inferred from monitoring schemes (Borges et al. 2016) and from the ongoing habitat degradation due to invasions of alien plants (namely Hedychium gardnerianum) in at least two subpopulations (Caldeiras Funda e Rasa at Flores and Galhardo at Terceira) and soil erosion and degradation due to soil trampling by dairy cows (Topo, S. Jorge). Current Population Trend: Decreasing.

Habitat and Ecology

The species is restricted mostly to hyper-humid, high elevation native forests dominated by Juniperus brevifolia and is particularly abundant in a few remnants of high elevation native grasslands, building its sheet weaver web in the ground. The ground is usually covered with mosses (with the dominance of Sphagnum spp. in some areas) and ferns. The species is active during the night. Based on data from SLAM traps (Borges et al. 2017) the species is mostly abundant in the summer months. Systems: Terrestrial.

Major Threat(s):

In the past, the species has probably strongly declined due to changes in habitat size and quality (Triantis et al. 2010). However, the species seems to have survived in the some native and grassland forests of the Azores, mostly at high elevation pristine sites. The main current threats are: a) the spread of invasive plant species namely Hedychium gardnerianum, which is changing the structure of the forest and the cover of endemic trees and shrubs; b) soil erosion due to trampling by dairy cattle (cattle are entering the native areas in S. Jorge island without control by the Conservation Managers). Based on Ferreira et al. (2016) the habitat will further decline as a consequence of climate change (increasing number of droughts, and habitat shifting and alteration). 

Conservation Actions

The species is not protected by regional law, but its habitat is in regionally protected areas (Natural Parks of Flores, Pico, São Jorge, Terceira and S. Miguel). Degraded areas, degraded due to invasive plant species (particularly in Caldeiras Funda e Rasa at Flores and Galhardo at Terceira) should be restored and a strategy needs to be developed to address the current threats from invasive species and trampling by cows, and the future threat from climate change. Formal education and awareness are needed to allow future investments in restored habitats invaded by invasive plants; while further research is needed into its ecology and life history in order to find additional specimens in more sites within the current range dominated by native forest and obtain adequate information on population size, distribution and trends. An area-based management plan is also necessary for the most disturbed sites, including invertebrate monitoring to contribute to a potential species recovery plan. Monitoring every ten years using the BALA protocol will inform about habitat quality (see e.g. Gaspar et al. 2011).