Red List of South African Species

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Critically Endangered (CR)
Assessors: David Edge
Facilitators: Mark Williams
Reviewers: Silvia Kirkman Domitilla Raimondo Rolf Oberprieler

Rationale (Changed due to Same category and criteria)

A highly restricted endemic to the Western Cape Province, South Africa (EOO 4 km<sup>2</sup>, AOO 20 km<sup>2</sup>). This species has been in decline ever since it was originally discovered on the West Coast in 1947. The last West Coast subpopulation at Pella Mission near Mamre became extinct in the 1990’s. Fortunately, <i>C. dicksoni</i> was discovered close to Witsand near the mouth of the Breede River in the 1980’s and Ernest Pringle later found a "strong and viable colony" (Pringle, 1990), which was to the north of Witsand. However, the two subpopulations in the Witsand area are all in decline and subjected to several threats, mainly due to alien invasive plants and overgrazing by domestic livestock. There are two locations, separated by about 3 km of wheat fields. Exchange of individuals from the northerly subpopulation is infrequent but possible, since it is at the limit of the dispersal range of the species. So they cannot be deemed to be "severely fragmented". The more southerly location, near Witsand itself, has more severe threats and this subpopulation fluctuates from year to year, sometimes being zero, causing extreme fluctuations in the overall EOO and AOO, as well as in the number of subpopulations and number of mature individuals. Furthermore, the overall population size is estimated to be <250 adult individuals. Approximately 95% of the individuals are in the more northerly subpopulation. This species therefore qualifies as Critically Endangered under criteria B and C.

Distribution

Endemic to the south coast of the Western Cape Province in South Africa, currently extant in the vicinity of Witsand at the Breede River mouth. Locally extinct on the West Coast, where it used to occur from Melkbosstrand to the Mamre area and also at Philadelphia.

Decline

From observations between 2009 and 2017 of the two Witsand subpopulations, the overall population fluctuates.

Historically, this species lost most of its habitat in the past from crop cultivation in the Swartland and the lower Breede River region, coastal developments on the west and south coasts, and alien invasions of the remaining habitat fragments. Current threats to its remaining habitat are ongoing alien plant invasions (Acacia cyclops) and grazing by domestic livestock.

Population trend

Trend

From observations between 2009 and 2017 of the two Witsand subpopulations, the overall population fluctuates. The largest (northerly) subpopulation occurs on the Westfield farm and the neighbouring farm to the north (Vondeling), and appears to have a good chance of long term survival if the habitat is correctly managed. A smaller subpopulation occurs closer to Witsand, about 3 km south of Westfield, separated from the larger subpopulation by wheat fields. Exchange of individuals from the northerly subpopulation is infrequent but possible, since it is at the limit of the dispersal range of the species. This subpopulation fluctuates considerably from year to year and it depends on immigration from the northerly subpopulation.

Threats

At Witsand, the Vondeling part of the northerly subpopulation is owned by a very co-operative farmer who has managed the habitat well, eradicating alien plants and only allowing light grazing by Bontebok and some cattle. There is no guarantee this situation will continue. The Westfield farm south of this has not been well managed, and there is a severe threat from proliferation of Rooikrans (<i>Acacia Cyclops</i>). An eradication program is underway to control and eventually eliminate this threat. Another threat at Westfield is grazing of domestic livestock, but the farmer has agreed to exclude such livestock for the time being. Negotiations are nearing completion to declare the whole of the Westfield farm near Witsand as a contract nature reserve managed by CapeNature. When a contract nature reserve is established aliens will be eradicated and only low density populations of indigenous herbivores (e.g. Bontebok, Eland) will be allowed. The subpopulation closer to Witsand is badly degraded, with ongoing threats from excessive sheep grazing and alien plants. It is hypothesised that the underlying reason for the decline on the West Coast may have been climate change, with steadily rising temperatures and drought deteriorating the remaining small patches of habitat not destroyed by urban growth and agricultural expansion or engulfed by the spread of alien vegetation.

Conservation

An intensive research programme was conducted by Dr D.A. Edge of LepSoc Africa, and articles on the ant/scale insect interactions and vegetation communities have been published. Alien vegetation clearance has been carried out from 2015 on the Westfield farm near Witsand, by CapeNature. The owner of Westfield, Stellenbosch University, has agreed to the entire farm (1 200 ha) becoming a contract nature reserve and negotiations are advanced to conclude this process.

References 

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 address = {Johannesburg &Cape Town},
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 year = {2013}
}
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 pages = {38--43},
 title = {The ants and scale insects on which the critically endangered <i>chrysoritis dicksoni</i> (Gabriel) (Lepidoptera: Lycaenidae: Aphnaeinae) depends for its survival.},
 volume = {26},
 year = {2016}
}
,@article{161336910,
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,@article{161336910,
 author = {Heath, A.},
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 volume = {25},
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}
,@article{161336910,
 author = {Heath, A. & Brinkman, A.K.},
 journal = {Metamorphosis},
 pages = {117--127},
 title = {Aspects of the life history, distribution and population fluctuations of <i>Oxychaeta dicksoni</i> (Gabriel) (Lepidoptera: Lycaenidae).},
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}
,@article{161336910,
 author = {Edge, D.A.},
 journal = {Metamorphosis},
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 title = {Vegetation associated with the critically endangered butterfly <i>Chrysoritis dicksoni</i> (Gabriel, 1947) (Lepidoptera: Lycaenidae: Aphnaeinae) at Witsand, Western Cape Province},
 volume = {27},
 year = {2016}
}
,@article{161336910,
 author = {Pringle, E.L.},
 journal = {Metamorphosis},
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 title = {Report on a recent trip to the south-west Cape, and on other matters.},
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}
,]
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