Conservation of endangered species

The conservation of species at risk often involves establishing protected areas and sometimes the translocation of individuals to new locations. Both approaches should be based on considerations of the niche requirements of the species concerned.

The overwintering habitat in Mexico is absolutely critical for the monarch butterfly (Danaus plexippus), which breeds in southern Canada and the eastern United States. The butterflies form dense colonies in oyamel (Abies religiosa) forests on 11 separate mountains in central Mexico. A group of experts was assembled to define objectives, assess and analyze the available data, and to produce alternative feasible solutions to the problem of maximizing the protection of overwintering habitat while minimizing the inclusion of valuable land for logging (Bojorquez-Tapia et al., 2003). As in many areas of applied ecology, ecological and economic criteria had to be judged together. The critical dimensions of the butterfly's overwintering niche include relatively warm and humid conditions (permitting survival and conservation of energy for the return north) and the availability of streams (resource) from which the butterflies drink on clear, hot days. The majority of known colony sites are in forests on moderately steep slopes, at high elevation (>2890 m), facing towards the south or southwest, and within 400 m of streams (Figure 7.5). According to the degree to which locations in central Mexico matched the optimal habitat features, and taking into account the desire to mimimize

Figure 7.5 Observed frequency distributions of 149 overwintering monarch butterfly colonies in central Mexico in relation to: (a) slope, (b) elevation, (c) aspect and (d) proximity to a stream. (After Bojorquez-Tapia et al., 2003.)

niche ecology and the selection of conservation reserves

Figure 7.5 Observed frequency distributions of 149 overwintering monarch butterfly colonies in central Mexico in relation to: (a) slope, (b) elevation, (c) aspect and (d) proximity to a stream. (After Bojorquez-Tapia et al., 2003.)

Figure 7.6 Optimal distribution in the mountains of central Mexico of overwintering monarch butterfly reserves (colored areas) according to three scenarios: (a) area constraint of 4500 ha,

(b) area constraint of 16,000 ha, and (c) no area constraint (area included is 21,727 ha). The orange lines are the boundaries between river catchment areas. Scenario

(c) was accepted by the authorities for the design of Mexico's 'Monarch Butterfly Biosphere Reserve'. (After Bojorquez-Tapia et al., 2003.)

Figure 7.6 Optimal distribution in the mountains of central Mexico of overwintering monarch butterfly reserves (colored areas) according to three scenarios: (a) area constraint of 4500 ha,

(b) area constraint of 16,000 ha, and (c) no area constraint (area included is 21,727 ha). The orange lines are the boundaries between river catchment areas. Scenario

(c) was accepted by the authorities for the design of Mexico's 'Monarch Butterfly Biosphere Reserve'. (After Bojorquez-Tapia et al., 2003.)

the inclusion of prime logging habitat, a geographic information system (GIS) was then used to delineate three scenarios. These differed according to the area the government might be prepared to set aside for monarch butterfly conservation (4500 ha, 16,000 ha or no constraint) (Figure 7.6). The experts preferred the no-constraint scenario, which called for 21,727 ha of reserves (Figure 7.6c), and despite the fact that their recommendation was the most expensive it was accepted by the authorities.

Unraveling the fundamental niche of species that have been driven to extreme rarity may not be straightforward. The takahe (Porphyrio hoch-stetteri), a giant rail, is one of only two remaining species of the guild of large, flightless herbivorous birds that dominated the prehuman New Zealand landscape (Figure 7.7). Indeed, it was also believed to be present distributions do not always coincide with optimal niche conditions

Figure 7.7 The location of fossil bones of the takahe in the South Island of New Zealand. (After Trewick & Worthy, 2001.)

Sims, Mansons, Bone Caves, Paturau-Heaphy River-

Honeycomb Hill-

Hodge Creek and Farriers Cave (Mt Arthur)'' Metro Cave

Anapai Rotokura

Murchison Mountains (extant population)

Anapai Rotokura

Murchison Mountains (extant population)

Wairau

Marfells Beach Waiau

Weka Pass Timpendean Waipara Pyramid Valley Waikari Cave

Greenhills

Wairau

Marfells Beach Waiau

Weka Pass Timpendean Waipara Pyramid Valley Waikari Cave

Opihi River, Totara Valley

Kings Cave

Tuarangi Stn sites

Mt Harris, Kapua

Ngapara/Totara

Swamp, Enfield

Ototira Awamoa

Macraes

Warrington, Waitati Long Beach, Kaikais Beach

Pahia Wakapatu Colac Bay

Greenhills

-False I. IPounawea Cannibal Bay xTokanni Mouth Forest Hill I McKerchers Cave extinct until the discovery in 1948 of a small population in the remote and climatically extreme Murchison Mountains in the southeast of South Island (Figure 7.7). Since then intense conservation efforts have involved habitat management, captive breeding, wild releases into the Murchison Mountains and nearby ranges, and translocation to offshore islands that lack the mammals introduced by people that are now widespread on the mainland (Lee & Jamieson, 2001). Some ecologists argued that because takahe are grassland specialists (tall tussocks in the genus Chionochloa are their most important food) and adapted to the alpine zone they would not fare well outside this niche (Mills et al., 1984). Others pointed to fossil evidence that the species was once widespread and occurred mainly at altitudes below 300 m (often in coastal areas - Figure 7.7) where they were associated with a mosaic of forest, shrublands and grasslands. These ecologists argued that takahe might be well suited for life on offshore islands that are free of mammalian invaders. It turned out that the sceptics were wrong in thinking that translocated island populations would not become self-sustaining (takahe have been successfully introduced to four islands), but they seem to have been right that islands would not provide an optimal habitat: island birds have poorer hatching and fledging success than mountain birds (Jamieson & Ryan, 2001). The fundamental niche of takahe probably encompasses a large part of the landscape of South Island, but the species became confined to a much narrower realized niche by people who hunted them, and by mammalian invaders such as red deer (Cervus elaphus scoticus) that compete with them for food and stoats (Mustella erminea) that prey upon them. The current distributions of species like takahe, which have been driven very close to extinction, may provide misleading information about niche requirements. It is likely that neither the Murchison Mountains nor offshore islands (with pasture rather than tussock grasses) coincide with the optimal set of conditions and resources of the takahe's fundamental niche. Historical reconstructions of the ranges of endangered species may help managers identify the best sites for reserves.

from land that had previously been 'improved' for pasture or used for arable farming. They wished to relate plants' performances to their life histories. On the basis of the results of the first 4 years of restoration, they calculated a performance index for commonly sown grasses (13 species) and forbs (45 species; forbs are defined as herbaceous plants that are not grass-like). The index, calculated for each of the 4 years, was based on the proportion of quadrats (0.4 X 0.4 m or larger) that contained the species in treatments where that species was sown. Their life history analysis included 38 plant traits, including longevity of seeds in the seed bank, seed viability, seedling growth rate, life form and life history strategy (e.g. competitiveness, stress tolerance, colonization ability (ruderality)) (Grime et al., 1988) and the timing of life cycle events (germination, flowering, seed dispersal). The best performing grasses included Festuca rubra and Trisetum flavescens (performance indexes averaged for the 4 years of 0.77); and among the forbs Leucanthemum vulgare (0.50) and Achillea millefolium (0.40) were particularly successful. Grasses, which showed few relationships between species traits and performance (only ruderality was positively correlated), consistently outperformed the forbs. Within the forbs, good establishment was linked to colonization ability, percent germination of seeds, fall germination, vegetative growth, seed bank longevity and habitat generalism, while competitive ability and seedling growth rate became increasingly important determinants of success with time (Table 7.3). Stress tolerators, habitat specialists and species of infertile habitats performed badly (partly reflecting the high residual nutrient availability in many restored grasslands). Pywell et al. (2003) argue that restoration efficiency could be increased by only sowing species with the identified ecological traits. However, because this would lead to uniformity amongst restored grasslands, they also suggest that desirable but poorly performing species could be assisted by phased introduction several years after restoration begins, when environmental conditions are more favorable for their establishment.

using knowledge of species traits... ... to restore grassland,...

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