The habitat in a multispecies context: one species’ matrix is another species’ habitat

4 Single Species versus Multispecies Conservation

4.2 The habitat in a multispecies context: one species’ matrix is another species’ habitat

As species have distinct resources, their habitats will be unique and their habitat bounds are likely to differ as a consequence, the more so as resources differ. Even for species sharing the same basic resource types, such as phy- tophagous insects exploiting the same host plant, there can be fundamental and striking differences in micro-resource requirements that affect distribu- tions and habitat suitability (e.g. saproxylic Coleoptera: Cerambycidae and Diptera: Syrphidae; Fayt et al., 2006). A classic cautionary tale is illustrated by the light conditions required for creating microstructures by larvae of the butterfly Limenitis camilla L. (Nymphalidae) on Lonicera percylmenum, very different from those required by the moth Hemaris fuciformis L. (Sphingidae) on the same plant (Fox, 2005). The probability of species having different habitat bounds increases when their resources fail to overlap or to intersect (discontinuous union). The structuring of resources and their connectivity

can potentially affect congruence in habitat bounds as much as does com- position (e.g. use of same host plant but in different settings; Gutiérrez et al., 2001). The probability of species’ habitat congruence is further reduced if their resources are associated with different vegetation units, as distinc- tions in vegetation units infer quantum shifts in resource types. One highly important generalization emerging from these percepts is the realization that one species’ matrix may well contain another species’ resources. As an axiom for conservation practice it may be somewhat less accurately but usefully restated to make the point as: one species’ matrix is another species’ habitat.

This can be tested. To provide an insight the example of the Great Ormes Head in North Wales (Cowley et al., 2000, 2001) can be taken. This headland has already been used as a template for mapping the metapop- ulation patches of several butterfly and moth species (e.g. Thomas and Harrison, 1992; Lewis et al., 1997; Gutiérrez et al., 1999; León-Cortés et al., 2000, 2003). Key amongst them is that of P. argus occupying calcicolous grassland (specifically parts of NVC categories CG1 and CG2; Stevens et al., 1995; see Table 5.2). A table of other NVC categories and land use types illustrates that one butterfly species or another has key resources in virtually every other vegetation or substrate unit (Table 5.2), including bare rock, mining spoil, scree and cliffs (Hipparchia semele L. Nymphalidae;

Dennis, 1977), and minor components, such as hedges, verges and sur- face excavations (e.g. P. tithonus,M. jurtina; R. Dennis, personal observa- tions). Substrates thought to be of little inherent value none the less have a role: such are walls of buildings in built up areas used by nymphalids (e.g.Vanessa atalanta L. and V. cardui L.) for thermoregulation and territo- rial perches, and intensively (sheep) grazed pastures walled off as farm- land used as breeding sites for other nymphalids (e.g. nettle patches for Aglais urticae L. and I. io L.; thistle patches for V. cardui). Even the most dis- turbed and eroded biotope, the grassland summit subject to severe human trampling, is used for mate location by hill topping species (Dennis and Dennis, 2006). The few vegetation and substrate units that could arguably be regarded as not forming parts of butterfly habitats are most certainly habitats for other organisms (e.g. a children’s play area on the summit has clumps of Marrubium vulgare L. (Lamiaceae) for the monophagous plume moth Wheeleria spilodactylus (Curtis) (Pterophoridae) (Menéndez and Thomas, 2000)); the sea cliffs exposed to sea spray are invaluable nesting sites for a variety of sea birds (e.g. Rissa tridactyla,Phalacrocorax carbo) with their associated beetle, fly and flea faunas (A. Fowles, personal communication) as is dense scrub for insectivorous birds (e.g. stonechats), which is also used as daytime shelter by the moth Idaea dilutaria (Hübner) (Geometridae). As it is, ensembles of Lepidoptera sharing the same host plant in the calcareous heath (e.g. Helianthemum larval feeders, such as P.

argus,Aricia agestis,Adscita geryon (Hübner) (Zygaenidae), and L. cornicu- latus larval feeders, such as Erynnis tages,Polyommatus icarus and Zygaena filipendulae; R.J. Wilson and C.D. Thomas, unpublished data; Gutiérrez et al., 2001) have very different distributions, indicative of differences in resources. Recent research has demonstrated that essential resources have

Table 5.2. Vegetation and other substrates on the Great Ormes Head, North Wales, UK and breeding resources for butterfl ies occupying the Carboniferous limestone headland.

Vegetation and substrate class^a Butterfl y species^c

CG1Festuca ovina–Carlina O. venata, C. croceus,P. argus,A. agestis,P. icarus,A. aglaja, vulgaris grassland L. megera,H. semele, P. tithonus, M. jurtina, A.

hyperantus, C. pamphilus

CG2Festuca–Avenula O. venata, C. croceus,P. argus,A. agestis,P. icarus,A. aglaja, pratensis grassland L. megera,H. semele,P. tithonus,M. jurtina, A. hyperantus,

C. pamphilus

CG6Avenula pubescens T. sylvestris, O. venata, C. croceus, A. agestis, P. icarus, grassland A. aglaja, L. megera, H. semele, P. tithonus,M. jurtina,

A. hyperantus, C. pamphilus

CG10Festuca ovina–Agrostis T. sylvestris, O. venata, C. croceus, P. icarus, A. aglaja, capillaris–Thymus praecox L. megera, H. semele, P. tithonus, M. jurtina, A. hyperantus,

grassland C. pamphilus

U4Festuca ovina–Agrostis T. sylvestris, C. croceus, P. icarus, V. cardui, A. aglaja, capillaris–Galium saxatile L. megera, H. semele, P. tithonus, M. jurtina,C. pamphilus grassland

MG1Arrhenatherum elatius T. sylvestris,O. venata, C. croceus, P. icarus, V. cardui, grassland A. aglaja, L. megera, H. semele, P. tithonus,M. jurtina,

A. hyperantus, C. pamphilus

MG6Lolium–Cynosurus T. sylvestris, C. croceus, L. phlaeas,P. icarus, V. atalanta, grassland (semi-improved V. cardui, A. urticae, I. io, L. megera, H. semele, P. tithonus, grassland; cemetery) M. jurtina, C. pamphilus

MC4Brassica oleracea maritime P. brassicae,P. rapae,P. napi cliff-ledge community

MC8Festuca rubra–Armeria P. aegeria, H. semele, P. tithonus, M. jurtina, C. pamphilus maritima maritime grassland^b

MC9Holcus lanatus maritime T. sylvestris, P. aegeria, L. megera, H. semele grassland^b

M24Molinia–Cirsium dissectum O. venata,M. jurtina fen meadow^b

H8Calluna vulgaris–Ulex O. venata, A. agestis, P. icarus, A. aglaja, H. semele, P. tithonus, gallii heath M. jurtina,C. pamphilus

Brachypodium sylvaticum O. venata, P. aegeria, L. megera, A. hyperantus grassland^b

H10Calluna vulgaris–Erica T. sylvestris, P. icarus, A. aglaja, L. megera, H. semele, cinerea heath P. tithonus,M. jurtina,C. pamphilus

‘CGH’ calcicolous grass heath T. sylvestris, C. croceus, P. argus, A. agestis, P. icarus, A. aglaja, L. megera, H. semele, P. tithonus,M. jurtina,C. pamphilus U20Pteridium aquilinum– T. sylvestris,O. venata,A. aglaja, H. semele, P. tithonus,

Galium saxatile community M. jurtina, C. pamphilus (dense bracken)

Scrub (Ulex europaeus, O. venata, L. phlaeas, P. aegeria,P. tithonus, M. jurtina Rubus spp.)

Woodland P. c-album, P. aegeria

Exposed rock (cliffs, crags, P. napi, C. argiolus, V. atalanta, L. megera, H. semele pavement, erosion scars,

scree, quarries, rock walls)

even been omitted from metapopulation patchworks for at least one of these species (e.g. contiguous shrubs and bracken are essential roosts, mate location sites and thermoregulation sites for P. argus; Dennis, 2004b;

Dennis and Sparks, 2006). These few examples do not begin to impress the full extent of the observation, that there is not an organismal empty space on the headland that can be dismissed as an empty set. The more species there are, the more the entire landscape becomes relevant for conservation.

All this is grist to the argument for moving to a resource-based view of landscape: merging patch and matrix.

There are, however, situations in which this variation in resource geog- raphy is so dramatically reduced that there is some excuse for considering a part of a landscape as an empty set, but this discounts restoration of the matrix (see below). Current fragmentation of landscapes, with intensive agricultural practices, leads to smaller patchworks and inevitable homo- genization of vegetation units. What tends to get left behind is not an unbi- ased sample of the original vegetation or substrates but that which is least valuable for human exploitation. As semi-natural vegetation units become reduced in size and homogenized, there is increased probability that spe- cies will share much the same habitat bounds. But, there is still an issue of whether they share the same fine-scale substrates within single vegetation units, a level below any of the most detailed mapping programmes (e.g. 10 × 10 m). Each substrate or vegetation subunit has its own dynamics and con- gruence in habitat boundaries is not synonymous with identity in resource use and lifespan. There is clearly much to test with the new resource-based habitat definition in a multispecies context. As part of this, there is an urgent need to develop techniques for identifying resource use in numerous species Table 5.2. Continued

Vegetation and substrate class^a Butterfl y species^c

Amenity (improved) grassland V. atalanta,V. cardui,A. urticae,I. io,P. c-album (playing fi elds; intensely

used farmland)

Urban and gardens G. rhamni,P. brassicae,P. rapae,P. napi,A. cardamines, C. argiolus,V. atalanta,V. cardui,A. urticae,I. io, P. c-album,P. aegeria, H. semele, P. tithonus Hedges, ditches, verges, tracks, T. sylvestris, O. venata,P. napi,L. phlaeas, C. argiolus,

paths, banks, springs A. urticae,I. io,P. aegeria,L. megera

aMainly UK national vegetation classifi cation (NVC) categories mapped for the headland by D.G. Guest and S.L.N. Smith in 1994 (Countryside Council for Wales, Bangor; www.ccw.gov.uk/) (Stevens et al., 1995);

note, some do not entirely match NVC classes (e.g. CG2, H8, Brachypodium sylvaticum grassland).

bVegetation units covering small areas.

cButterfl y species recorded having host plants in >50% quadrats. Bold, suitable breeding biotope, most supported by observations of egg laying and occurrence of both sexes (R. Dennis, personal observations).

Nectar and utility resources not disclosed but ensure wider use of vegetation and substrate on the headland than listed (see text).

(Dennis, 2004a), as well as generating principles of resource impact on spe- cies other than area and isolation.