Lepidoptera conservation in urban environments: theory and practice.
Increasing proportions of Earth's burgeoning human population dwell in cities and towns, with these continually expanding and becoming more intensively developed at the expense of more natural environments and the biodiversity they support. 'Megacities' are forecast to increase in number and size, with the current largest (Greater Tokyo, with more than 35 million people within a conurbation of 13 cities) perhaps becoming emulated elsewhere. Collectively, the changes to more natural environments as increasing amounts of periurban land are engulfed for housing, industry and the supporting infrastructure (such as transport systems, water provision, waste disposal and recreational amenities) needed to sustain people, are one of the most serious global threats to numerous local and endemic animals and plants. In parallel with agroecosystem establishment and maintenance, the massive, often abrupt, changes to the parental environments during urbanisation cause direct losses of more natural biotopes and allow proliferation of alien species and their impacts, with those effects also extending to freshwater bodies, such as through run-off and pollution, and in some cases also affecting adjacent coastal areas.
In addition to these two universal and pervasive complexes of threat (habitat loss and degradation and impacts of alien invasive species), a number of more particularly 'urban threats' arise, some with serious consequences for native insects. As examples, paved surfaces (concrete, asphalt) directly remove habitat needed by ground-nesting bees and other insects; asphalt roads can induce misorientation of aquatic insects to polarised light, leading to futile oviposition on road surfaces; traffic can cause direct mortality; roadways may act as a barrier, isolating insect populations; light intensity in streets and buildings can attract phototactic insects from more natural areas and render them vulnerable to vertebrate predators; and 'heat islands' may affect development rates and tolerances of resident and adventive species. All these effects are discussed in a recent overview (New 2015) and are noted here simply as background to the complexity of appraising threats for any given urban insect assemblage or species. The collective consequences include many losses of species or populations, changes in composition of assemblages and communities, with changes in ecological functions due also to novel interactions from invasive alien species. The widespread trend toward biotic homogenisation, as resident or endemic ecological specialist species and restricted ecosystems succumb to widespread invading generalists, including those deliberately introduced, emphasises the importance of conservation in urban environments as a central arena for many components of biodiversity to persist. Many native biota are restricted progressively to small remnant fragmented sites in which populations are increasingly vulnerable and isolated by largely inhospitable surrounding terrain, and their natural population structure disrupted. Many formerly widely distributed insects have little natural habitat and resources left in now-urban areas, and persist only on isolated and degraded remnant sites within the urban milieu.
Studies on selected insect groups (notably ants, bees, ground beetles and butterflies) along urban-rural gradients and in urban sites have (1) shown the changing relative presence of 'urbanophobes' and 'urbanophiles' and their ecological characteristics, and so (2) provided background for understanding the changes that occur and the needs and methods for prevention and remediation of changes and losses, as practical conservation. Butterflies and other Lepidoptera such as diurnal moths are a potent insect flagship group, contrasting with most other insects in their wide public appeal and acceptance that they are worthy of conservation. This sympathy is accompanied by reliable species-level taxonomy, considerable biological knowledge, and awareness of the factors that constitute threats or that influence their wellbeing. Close association of many species with specific vegetation (as larval food and adult nectar sources) provides a tangible framework for defining critical resources, with their provision and accessibility a major component of practical conservation. Many species have become demonstrably threatened by urbanisation. Many conservation programs for threatened urban butterflies have been undertaken, especially in the temperate northern hemisphere. This paper illustrates some of the varied contexts in which Lepidoptera conservation needs have arisen in urban areas of eastern Australia, and the scope of species management plans for three key species: Eltham copper butterfly Paralucia pyrodiscus lucida; Richmond birdwing butterfly Ornithoptera richmondia; and Golden sun-moth Synemon plana).
Contexts and cases
The varied ecology of butterflies and moths, and the varying processes contributing to habitat loss and change in urban areas, ensure that each individual species may have rather different combinations of threats and conservation needs within the individual regional pattern of ecosystem change. The three Australian species discussed briefly below illustrate this variety. Synthesis from these and others helps to establish general conservation principles with wide application in urban environments. The two contrasting butterflies are subjects of the longest-running insect conservation campaigns in Australia, and have attracted much official attention and public support, with 'citizen science' campaigns integrated into wider conservation management. Their importance and conservation strategies are summarised by New (2011, Eltham copper) and Sands and New (2013, Richmond birdwing). The concern for the third example, the Golden sun-moth, is more recent, and has wide ramifications for urban development, through its role in confrontations between land developers and conservationists seeking to protect remnant native grasslands close to some major settlements, most notably on periurban areas scheduled for new suburbs and industrial parks close to Melbourne, Victoria (New 2014). Their differing urban contexts are outlined below. All are endemic ecological specialists with biological requirements that render monitoring and management complex, and all are formally protected taxa in Australia.
The Eltham copper butterfly Paralucia pyrodiscus lucida Crosby (Lycaenidae)
The few remnant populations of this locally endemic subspecies near Melbourne each occur on small (ca 1-2 ha) remnant open eucalypt woodland patches to which they have been confined by housing developments. Each population is isolated by housing and roads, and sites are subject to successional changes, weed invasions, run-off from nearby roads, and general disturbance. Larvae feed only on Sweet Bursaria Bursaria spinosa Cav. and are tended obligatorily by ants (Notoncus spp.); they feed nocturnally and are 'herded' up Bursaria by ants, and shelter by day in the subterranean ant nests near the plants. Conservation, undertaken continuously since 1987, focuses on site protection and resource supply. Each site has individual needs, so that management is necessarily long-term and intensive, and the butterfly is conservation-dependent. It also has significant flagship value within the local community and has been adopted widely as a local 'icon'. Management to regenerate succession, control invasive weeds, reduce ground debris and open up the tree canopy to benefit low-growing Bursaria has included control burns orchestrated to cause minimum harm to the butterfly. Extensive community participation (led by an active Friends of the Eltham Copper group) and education, through local primary schools and others, have been continually and strongly supported by local authorities. The practical support of volunteers has been instrumental in conducting annual larva counts at night, and conducting daytime transect surveys for adult butterflies, as well as in practical management such as weed and rubbish removal from sites. The novelty of the tripartite association ('plant-butterfly-ant') has considerable public and educational appeal.
The Richmond birdwing butterfly Ornithoptera richmondia (Gray) (Papilionidae)
This strongly flying forest birdwing was previously distributed widely along coastal regions of southern Queensland and northern New South Wales but disappeared from most of this range (including the city of Brisbane, where it was formerly common) during the 20th century. The two reasons for this decline are (1) clearing of native vegetation for urban or agricultural conversion, with direct loss of habitat in and around settlements, and (2) the importation and spread of an alien South American vine (Aristolochia elegans Mast), initially a garden ornamental but subsequently widespread in natural areas. The vine attracts female birdwings to oviposit, but the foliage is toxic to developing larvae, which die after feeding. Conservation has focused on the twin activities of removal of the alien vine and extensive replacement and augmentation plantings of the native food plant, Pararistolochia praevenosa (F. Muell.) M.J.Parsons. The conservation program, undertaken since the late 1980s, has embraced the entire historical documented range of the butterfly but with a strong focus on urban areas such as Brisbane, with continued support of local people and schools in both the above activities. Planting of nursery-propagated P. praevenosa has emphasised (1) enhancement of these in remnant sites, including any occupied by the birdwing, and (2) planned plantings in natural corridors, to link those sites in the expectation that the birdwing may progressively and naturally re-colonise. Vines have also been planted in many home and school gardens, where they are monitored continually for the butterfly or its conspicuous larvae. Early appeal of the project is indicated by more than 29 000 vines being distributed by 1998, with more than 420 schools involved in the project, and coordinated through the national CSIRO Double Helix Science Club for young people. More recent community activities are coordinated and publicised through the Richmond Birdwing Conservation Network, through activities such as an informative newsletter, meetings and workshops.
The Golden sun-moth Synemon plana Walker (Castniidae)
Representing an endemic group of diurnal moths, Synemon plana occurs on remnant native grasslands, regarded as one of Australia's most endangered ecosystems on the southeastern mainland. The major conservation emphasis is to prevent remaining grassland from undergoing development in the face of severe pressures for land resumption for housing (including entire new suburbs) and industry, especially near Melbourne. The sun-moth is one of a small portfolio of flagship species in this wider conservation endeavour. The moth's unusual biology makes populations very hard to assess or even detect--larvae feed underground, so are largely inaccessible for sampling, and adults are short-lived (1-5 days), do not feed, and emerge continuously over a flight season of about 8-10 weeks on any site. Only males fly readily, and females are much less active. Additional complications are that the generation time is unknown, suggested to be one, two or three years, and that moths fly only under particular weather conditions and for a few hours in the middle of the day. This may be offset by monitoring empty pupal cases that protrude from the ground and persist for three weeks or more (Richter et al. 2013). In short, population assessments and detecting the moth require repeated visits over a season, by people who are aware of the sampling uncertainties involved, and preferably over several years to detect annual cohorts of a possible non-univoltine development pattern. Such protracted evaluations are contrary to the needs of developers seeking rapid approval for their activities to proceed. Inspection of grassland sites for the sun-moth (which is designated nationally as 'critically endangered') is mandatory in environmental impact assessments, with formal guidelines for the procedures and a detected population of five male moths triggering the need for further investigation as well as the possibility of designating habitat offsets if the project is to proceed. Extensive public concern and publicity for the moth has occurred. Management is further complicated by the implication that larvae may use the declared noxious weed Chilean Needle Grass Nassella neesiana (Trin. & Rupr.) Barkworth as an important food resource on some sites.
The above examples help to display the variety of contexts that lead to the need for urban conservation of individual species of Lepidoptera. Further details for each are available from the references listed.
The Eltham copper exemplifies that some taxa can be conserved only by focusing on single small remnant sites embedded within a largely inhospitable matrix. These taxa are essentially conservation-dependent, imposing intensive and expensive continuing conservation management if they are to persist. There is little likelihood of the various Eltham copper habitat patches near Melbourne becoming functionally contiguous, and the greater likelihood is that some populations may already be in an extinction debt phase because of their very small size. If so, their demise from such small populations (or residual metapopulation units) may be hastened by stochastic events. At present, management continues on all occupied sites, with the aim of ensuring conditions suitable for the butterfly, its attendant Notoncus ant, and Bursaria within the natural vegetation community that includes other notable species such as some rare orchids. That approach incorporates continuing site protection and alleviating and preventing further threats, in the context of sustaining long-term suitability of those sites as natural succession occurs. The program depends on continued support from local government and people, both of which are universally essential in insect species conservation programs, together with education and publicity to foster interest among young people.
The wider perspective engendered for the Richmond birdwing is of a wide-ranging, landscape-focused conservation program that still incorporates focal sites, but largely in the context of their roles in enhancing local richness as nodes in promoting connectivity through corridors. This contrasts with the above primary focus on site dependence. Restoration of degraded habitat (removal of the alien larval food plant) and extension of overall occupiable area by providing critical resources (planned plantings of the natural larval food plant) are the twin major activities of a program with massive public appeal. The actions needed are easy to understand and execute, and the spectacular butterfly is easy to detect and monitor. Range extension is by natural flight dispersal, rather than any deliberate translocation, a tool sometimes used for less vagile species.
Both the butterflies discussed above exemplify the very common scenario of increasing the value of occupied sites by measures such as legal protection, resource enhancement, removal and prevention of threats, and promoting connectivity where possible. The emphasis on restoration changes for the Golden sunmoth, with the primary aim to protect existing inhabited remnant grassland areas in the face of developer pressures that could lead to their rapid loss, is a scenario of political and economic conflict with the potential to affect urban planning as demand for building sites increases into periurban areas. There are many parallels elsewhere in the world.
The three scenarios exemplified by these species thus differ in scale and focus, but with the commonality of urban involvement, with past or continuing urbanisation being the primary threats to each taxon. They emphasise the importance of understanding the biology of the focal species as a basis for effective management, the landscape context of conservation need, combined with the security of focal sites and the need for long-term and effective monitoring and adaptive management. Education and involving the local community, both as young people and as citizen scientists, in any such program is vital, together with effective communication and coordination of conservation activities in the long-term, sometimes over decades.
Urban environments create many needs for conservation, but also many opportunities for this to occur. The vast variety of urban 'open spaces', from large parks, remnant reserves and brownfield sites to small home gardens and novel habitats such as 'green roofs' can in many cases be manipulated to harbour increased native biodiversity, or foster wellbeing of focal threatened species. By increasing floral and structural diversity, as the most manipulable environmental features with which numerous insects (including most Lepidoptera) associate, local community richness and assemblage composition can be both protected and enhanced. Such measures include active protection of natural urban remnant sites and promotion of less intensive management of open spaces (e.g. by decreasing sanitation measures by reducing mowing frequency and leaving some weedy plants in parks or flowerbeds). These are all activities in which Lepidoptera can become significant umbrella taxa, accepted as such across these spatial scales by both 'top-down' (local government or other agency) and 'bottom-up' (individual householders or neigh bourhood groups) managers. The latter, for example, may create 'butterfly gardens' and/or become involved in local issues, and are exemplified well by the 'Friends' groups that support each of the species noted above.
Urban environments present abundant opportunities to harmonise insect conservation with human recreational and amenity needs. These can be undertaken in conjunction with wise urban planning and landscape design to promote connectivity between open spaces, and in combination with surveys to determine the extent and needs of native biodiversity. The urban arena is a vital component of conserving our natural biological heritage. Lepidoptera, whether considered as individual threatened taxa or as conspicuous and relatively easily studied assemblages in which reasons for change can often be defined, are important in wider urban conservation endeavours throughout the world.
This paper is based on a contribution to the 2015 FNCV Symposium on 'Impacts on Biodiversity during the Anthropocene'. I thank Max Campbell for his kind invitation to participate in this stimulating gathering.
Received 26 November 2015; accepted 4 August 2016
New TR (2011) Butterfly conservation in south-eastern Australia: progress and prospects. (Springer: Dordrecht).
New TR (2014) Lepidoptera and conservation. (Wiley-Blackwell: Oxford)
New TR (2015) Insect conservation and urban environments. (Springer: Cham)
Richter A, Weinhold D, Robertson G, Young M, Edwards T, Hnatiuk S and Osborne W (2013) More than an empty case: a non invasive technique for monitoring the Australian critically endangered golden sun moth, Synemon plana (Lepidoptera: Castniidae). Journal of Insect Conservation 17, 529-536.
Sands DPA and New TR (2013) Conservation of the Richmond birdwing butterfly in Australia. (Springer: Dordrecht)
Department of Ecology, Environment and Evolution, School of Life Sciences, La Trobe University, Melbourne, Victoria 3086. Email: T.New@latrobe.edu.au
|Printer friendly Cite/link Email Feedback|
|Publication:||The Victorian Naturalist|
|Date:||Oct 1, 2016|
|Previous Article:||Places, people and events: a reading on the 20th anniversary of the opening of the FNCV premises in Blackburn, 8 July 2016.|
|Next Article:||Towards an ecologically sustainable fire management strategy.|