BIOLOGICAL CONSERVATION 136 (2007) 552– 562 available at www.sciencedirect.com journal homepage: www.elsevier.com/locate/biocon Population viability of the narrow endemic Helianthemum juliae (CISTACEAE) in relation to climate variability Manuel V. Marrero-Go´meza, J. Gerard B. Oostermeijerb, Eduardo Carque´-A´ lamoa,A´ ngel Ban˜ ares-Baudeta,* aParque Nacional del Teide, Calle Emilio Calzadilla, no. 5 – 4°Izq 38002, Santa Cruz de Tenerife, Canary Islands, Spain bUniversity of Amsterdam, Institute for Biodiversity and Ecosystem Dynamics, Kruislaan 318, 1098 SM Amsterdam, The Netherlands ARTICLE INFO ABSTRACT Article history: Narrow endemic plants are highly vulnerable to extinction as a result of human distur- Received 27 June 2006 bance and climate change. We investigated the factors affecting the population viability Received in revised form of Helianthemum juliae, a perennial plant endemic to the Teide National Park on Tenerife, 2 January 2007 Canary Islands. One population was demographically monitored from 1992 to 2001 and Accepted 5 January 2007 analysed using matrix projection models to determine finite rates of increase and critical stages in the life cycle. Lambda values varied between 0.697 and 1.740, and were highly pos- itively correlated with annual precipitation, but not with temperature. Survival of adults Keywords: had the highest elasticity, and summed elasticities of the growth and fecundity transitions Endangered plants correlated positively with lambda and precipitation. Most of the mortality in the population Extinction seemed drought-related, and no other threats were identified. Deterministic simulations PVA showed population increase, but introducing environmental stochasticity by modelling Population dynamics variation in precipitation from existing data of the past 85 years revealed high extinction Conservation probabilities (0.74–0.83 in the next 100 years). This plant is likely to be at risk under scenar- Global warming ios of global warming. Our simulations suggest that augmenting the population would only Canary islands delay extinction. A more viable option for long-term conservation seems to be the introduc- tion of populations at more humid locations within the Teide caldera. Ó 2007 Elsevier Ltd. All rights reserved. 1. Introduction always received special attention from conservation organi- zations. This is certainly true for geographically highly One of the main tasks of the conservation botanist is to pro- restricted endemic plants, which are exceptional representa- tect endangered plant species from extinction. In a way, all tives of certain regions. In many cases, the presence of such plants face the risk of extinction due to various causes, such species has been the motivation for the founding of national as habitat destruction, habitat fragmentation, displacement parks, such as the Sierra Nevada National Park in Spain (Bo- by or hybridization with invasive exotic species, climate letı´n Oficial del Estado, 1999). It is therefore not surprising change, overharvesting for economic purposes, etc. (Ooster- that the conservation of endemic plant species often has meijer, 2003). Rare plants, however, are particularly sensitive very high conservation priority in such parks (Marrero to these threats, because of their restricted distribution and et al., 2003a). low numbers of populations and individuals (Goodman, Yet, it is not always clear whether endemic species are in 1987; Menges, 1991). Because of this vulnerability, they have need of intensive conservation management (Ban˜ ares et al., * Corresponding author: Tel.: +34 922290129; fax: +34 922244788. E-mail address: [email protected] (A´ .Ban˜ ares-Baudet). 0006-3207/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.biocon.2007.01.010 BIOLOGICAL CONSERVATION 136 (2007) 552– 562 553 2001). After all, they have survived in their restricted distribu- del Obispo populations are located on small rocky ledges over tion areas for very long time periods without any special care, an area of 300 m2; the Risco Verde population is found on deb- so why should they need any now? It is clear that when they ris at the base of cliffs covering a surface of 200 m2. are subjected to any threats imposed by human actions (hab- At a distance of 800 m from the Can˜ ada de las Pilas pop- itat destruction and fragmentation, invasive exotic species, ulation, an experimental introduction (sensu Falk et al., overharvesting, etc.), conservationists should focus on 1996) was established in Can˜ ada de Diego Herna´ndez in removing these threats as soon as possible. However, when 1989–1990. The introduction comprised a total of 350 human threats are not so obvious, as is the case with the ef- three-year old plants, planted over an area of 500 m2, which fects of climate change for example, removing them is also were grown ex situ from seeds collected in the Can˜ ada de las less straightforward (Oostermeijer, 2003). Pilas population. In 1992, 122 plants had survived and abun- Assessing the impact of different threats on the survival of dant recruitment by seedlings was observed. In this year, populations is the main aim of population viability analysis, the population was designated for demographic monitoring or PVA. In this paper, we report on such a PVA for the plant in order to evaluate the success of the reintroduction and species Helianthemum juliae Wildpret (CISTACEAE), which is determine the factors that affect population viability in this unique to a very small area on the crater wall of the Teide Na- species. tional Park on Tenerife, Canary Islands, Spain. Specifically, we The local microhabitat differences are minimal among the ask the following questions: native and the reintroduced populations, especially in rela- tion with the factors that might affect soil water availability. (1) What is the risk of extinction of the study populations? The differences in altitude among the sites are less than (2) Which are the most critical life-stages in the life cycle? 100 m (2141–2236 m.a.s.l.), they all have a West-exposition (3) Which environmental variables are the most important (Azimuth 268–276°), the slope is similar (36–42°) and the sub- determinants of extinction risk? strate has identical characteristics: weakly developed soils (4) To what extent might climate variability have affected (Orthents) over salic geological materials. population dynamics in the past and how will it possi- bly affect future population viability? 2.2. Data collection and analysis (5) Which strategies are indicated for the conservation of this species? 2.2.1. Life stages Demographic censuses were made during 10 years. We in- A very useful tool to resolve these questions are stage- or stalled a 10 · 10 m2 monitoring plot protected with a 1.75 m size-structured matrix projection models, that can be con- high aluminium fence with the aim to exclude rabbit grazing. structed on the basis of medium- to long-term demographic All individuals were labelled with aluminium identification data (Menges, 1986; Morris and Doak, 1998; Caswell, 2001). If tags and were classified at each census in one of the following such data are available over a long period, it is possible to test four categories: Juveniles (small, vegetative individuals with a the relationships between demographic transitions and cli- height <15 cm and no signs of previous flower stalks); Vegeta- matic variables such as temperature and precipitation. For tive adults (individuals >15 cm with evidence of previous flow- H. juliae, we have performed demographic censuses for 10 er stalks but vegetative at the moment of censusing), young years between 1992 and 2001, and obtained 85 years of cli- reproductive adults (plants <20 cm tall with flower stalks) and mate data from a nearby meteorological station. mature reproductive adults (>20 cm tall with flower stalks). In the beginning, the plot enclosed 22 mature reproductive 2. Materials and methods adults, seven young reproductive adults, 10 vegetative and seven juvenile individuals. 2.1. Species and study area We devised this stage classification to characterize the population using a biological approach (Lefkovitch, 1965; Wer- The genus Helianthemum is represented on the Canary Islands ner, 1975), which relies on field observations of developmen- by 12 species, of which 7 are endemic to this archipelago tal states. First, individual plants were classified in the basic (Hansen and Sunding, 1993). They colonize most of the eco- stages, i.e. juveniles, vegetative and reproductive individuals. systems existing on these islands; from the xerophytic coast- Later, the reproductive individuals were divided into two cat- al landscapes to the high mountain shrublands. H. juliae is a egories based on the intensity of flowering. The first class small iteroparous shrub that is endemic to the high mountain (young reproductive adults) comprises the adults in their first ecosystem of Tenerife (Canary Islands). Adult plants are up to or second year of flowering. They have a small size (<20 cm) 30 cm tall and produce between 5 and 40 flower stalks with and produce less than 50 flowers. The second class (mature yellow flowers from their third or fourth year onwards. The reproductive adults) includes the larger plants (P20 cm tall) average fruit contains 45 seeds. The average life span of indi- with more than 50 flowers. This subdivision was based on vidual plants is relatively short (14 years). field observations of growth and survival rates of reproductive H. juliae is considered critically endangered (CR) (Marrero adults. We did not consider a seed stage because seeds germi- et al., 2003b). Only three small populations are known from nated directly after dispersal, so we assumed a short-lived the wall of the Can˜ adas del Teide caldera (Fig. 1): Can˜ ada de seed bank. Hence, introducing seeds into the life cycle model las Pilas (43 adults), Risco Verde (25 adults) and Mesa del Obis- would introduce a time-lag (Caswell, 2001). We recorded the po (49 adults). Globally, the species has only 868 individuals numbers of seedlings in the autumn and spring cohorts dur- (adults and immatures).