Scudder, G. G. E. 2010. Grasslands: Biodiversity Hotspots for Some Arthropods in British Columbia. In Arthropods of Canadian Grasslands (Volume 1): Ecology and Interactions in Grassland Habitats. Edited by J. D. Shorthouse and K. D. Floate. Biological Survey of Canada. pp. 121-134. © 2010 Biological Survey of Canada. ISBN 978-0-9689321-4-8 doi:10.3752/9780968932148.ch6

Chapter 6Grasslands: Biodiversity Hotspots for Some Arthropods in British Columbia

Geoffrey G. E. ScudderDepartment of Zoology, University of British Columbia

Vancouver, British Columbia, Canada V6T 1Z4

Abstract. This chapter reports on research into the potentially rare and endangered terrestrial arthropods in British Columbia to determine the rarity and richness hotspots for these species as well as those for terrestrial true bugs (Heteroptera: Prosorrhyncha), butterflies (Lepidoptera), and terrestrial neuropteroids (includes Neuroptera and Raphidioptera). The results are interpreted in relation to the distribution of natural low-elevation grasslands in the province. Conservation implications are discussed.

Résumé. Ce chapitre fait état des recherches effectuées sur les arthropodes terrestres qui pourraient être rares ou en danger de disparition en Colombie-Britannique afin de déterminer la rareté et la richesse des régions névralgiques de la biodiversité de ces espèces et d’autres espèces d’hémiptères terrestres (Heteroptera : Prosorrhyncha), de lépidoptères (Lepidoptera) et de neuroptéroïdes terrestres (y compris Neuroptera et Raphidioptera). Nous interprétons les résultats à l’aune de la répartition des prairies basses naturelles dans la province, et examinons leur signification du point de vue de la conservation.

Introduction

The term “biodiversity hotspot” was originally coined by Myers (1989, 1990) to indicate priority conservation areas of the world with a high number of endemic species. However, the term hotspot is now applied more generally to indicate geographical areas that rank particularly high in one or more axes of species richness, levels of endemism, number of rare species, and intensity of threat (Reid 1998).

Such biodiversity hotspots have now been identified in the British Isles (Prendergast, Quinn et al. 1993; Williams et al. 1996), Europe (Williams, Humphries et al. 2000; Komonen 2003; Gjerde et al. 2004), Africa (Pomeroy 1993; Williams, Wicz et al. 2000), the United States (Dodson et al. 1997), and elsewhere (Harcourt 2000; Roberts et al. 2002). Preliminary results on hotspot analyses in British Columbia have also been published (Scudder 2005).

Distribution of BC Grasslands

The distribution of the main natural low-elevation grassland areas in British Columbia is shown in Fig. 1. The most extensive areas are in the southern interior of the province, with lesser representation on the south coast and the northeast in the Peace River area. The distribution of grasslands in British Columbia used for this study is based on the Biogeoclimatic Ecosystem Classification described in Meidinger and Pojar (1991). Within

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this classification, Nicholson et al. (1991) document the distribution and community structure of the extensive grasslands of the bunchgrass zone (BG). However, natural low-elevation grasslands occur in other ecozones. Specifically, the Garry oak ecosystem in the dry areas of the coastal Douglas-fir zone (CDF) (Nuszdorfer et al. 1991) characteristically contains patches of grasslands. Furthermore, the ponderosa pine zone (PP) is open and park-like with a ponderosa pine (Pinus ponderosa P. and C. Lawson) canopy and an understory dominated by bluebunch wheat grass (Pseudoroegneria spicata (Pursh) A. Löve). These grasslands that occur throughout the PP are thought to have developed as a result of a combination of edaphic and topographic conditions, together with a history of fire (Hope, Lloyd et al. 1991).

This combination of conditions and fire history has likewise led to the development of large grassland areas in the interior Douglas-fir zone (IDF) (Hope, Mitchell et al. 1991). Grasslands also occur on the steep, south-facing slopes above the Peace River in the boreal white and black spruce zone (BWBS) (DeLong et al. 1991), in part of what Munro and Cowan (1947) call the Peace River Parklands. In addition, grassland patches occur on the south-facing slopes of the Stikine River near Telegraph Creek in the BWBS.

The BG, CDF, IDF, and PP were mapped by using data from the BC Ministry of Sustainable Resource Management website at ftp://ftp.elp.gov.bc.ca/dist/arcwhse/ wildlife/ (now available at the BC Ministry of Forests and Range at FTP://ftp.for.gov.bc.ca/HRE/external/!publish/becmaps/GISdata/CurrentVersion). The polygons for the south-facing slopes of the Peace River were mapped by using data from the Grasslands Conservation Council of BC, and the Stikine River section of the BWBS, as shown in Fig. 1, was added freehand.

Table 1. Terrestrial arthropod data (as of May 6, 2008)1 imported into WORLDMAP 1:20,000. Abbreviation: AAFC = Agriculture and Agri-Food Canada.

Data Set No. of Taxa No. of Records Data Source

Rarity Hotspots

Arthropods 669 9,514 G.G.E. Scudder (compilation)

Heteroptera 99 3,491 G.G.E. Scudder

Butterflies2 60 3,486 A. Jessop (AAFC), C. Guppy,J. Heron, N. Kondla

Neuropteroids 18 185 G.G.E. Scudder

Richness Hotspots

Heteroptera 623 32,458 G.G.E. Scudder

Butterflies 187 38,787 A. Jessop (AAFC), C. Guppy,J. Heron, N. Kondla

Neuropteroids 74 2,911 G.G.E. Scudder

1 Alien species excluded.2 Includes species and subspecies listed on the provincial Red list and Blue list by the BC Conservation Data Centre.

Grasslands: Biodiversity Hotspots for Some Arthropods in British Columbia 123

Georeferenced Distributional Data

Georeferenced distributional data were assembled for the rare species of terrestrial arthropods listed in Scudder (1994), as well as a few additional species added to this list since 1994. The distribution data for butterflies were obtained from the Butterflies of Canada database, supplemented by additional data from local lepidopterists.

The data for terrestrial Heteroptera and terrestrial neuropteroids were assembled by the author from the recent published literature and from an examination of material in most of the major entomological collections in Canada. Table 1 lists the number of taxa and

Fig. 1. Distribution of the main natural low-elevation grassland areas in British Columbia. Many of these areas are treed savanna or are developed for agriculture, houses, or other human uses.

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number of records involved in these databases. ArcView (version 3.2) software was used to map the location of the records in these taxonomic databases.

Hotspot analyses were undertaken by using WORLDMAP software that was made available and custom modified by Dr. P. Williams (Natural History Museum, London) for application in British Columbia. Analysis was done by using a 1:20,000 NTS grid with 7,056 grid cells in the province. ArcView software was then used to map the centroid of the top 5% of the hotspot grid cells on the grassland map layer.

The locations for the potentially rare and endangered terrestrial arthropods included in the analysis are shown in Fig. 2. The rarity hotspot analysis is depicted in Fig. 3 and shows that the majority of the top hotspots are in the southern interior and the southwest parts of the province. Figs. 4–6 show the separate rarity hotspot analyses for the rare Heteroptera, the rare butterflies, and the rare neuropteroids, respectively. Table 2 summarizes the distribution of the top 5% of the hotspots for these taxa, relative to the low-elevation grasslands in the province. The rare terrestrial Heteroptera have 78%, the rare butterflies 93%, and the rare neuropteroids 100% of the top 5% of the rarity hotspots in these grasslands. Potentially rare and endangered terrestrial arthropods have 55% of the top 5% of rarity hotspots in the grasslands.

The distribution of the full list of localities involved in the terrestrial Heteroptera database is shown in Fig. 7. Similarly, Figs. 8 and 9 represent the localities involved in the butterfly and neuropteroid databases, respectively. Figs. 10–12 present the centroid of the grid square for the top 5% of richness hotspots for the terrestrial Heteroptera, butterflies, and terrestrial neuropteroids.

Table 2. Top 5% grid cells within and outside of grasslands in British Columbia for terrestrial arthropods.

Results

Grid Cells within Grasslands

Grid Cells outside of Grasslands

Total Grid Cells Identified

for Top 5% RichnessNumber Percentage Number Percentage

Rarity Hotspots

Arthropods 18 55 15 45 33

Heteroptera 7 78 2 22 9

Butterflies 13 93 1 7 14

Neuropteroids 2 100 0 0 2

Richness Hotspots

Heteroptera 18 60 12 40 30

Butterflies 26 57 20 43 46

Neuropteroids 10 56 8 44 18

Grasslands: Biodiversity Hotspots for Some Arthropods in British Columbia 125

Fig. 2. Recorded localities for the rare terrestrial arthropods.

Fig. 3. Top 5% of hotspots for the rare terrestrial arthropods.

126 G. G. E. Scudder

Fig. 4. Top 5% of hotspots for the rare terrestrial Heteroptera.

Fig. 5. Top 5% of hotspots for the rare butterflies.

Grasslands: Biodiversity Hotspots for Some Arthropods in British Columbia 127

Fig. 6. Top 5% of hotspots for the rare terrestrial neuropteroids.

Fig. 7. Recorded localities for the terrestrial Heteroptera.

128 G. G. E. Scudder

Fig. 8. Recorded localities for the butterflies.

Fig. 9. Recorded localities for the terrestrial neuropteroids.

Grasslands: Biodiversity Hotspots for Some Arthropods in British Columbia 129

In the analysis of richness hotspots (Table 2), 60% of the top 5% of the terrestrial Heteroptera hotspots occur in the low-elevation grasslands, and 57% of the top 5% of butterfly hotspots occur in these grasslands. For terrestrial neuropteroids, 56% of the top 5% of the richness hotspots are also in these grasslands. The tabulation thus shows that there is little difference between the richness hotspot percentages for terrestrial Heteroptera, butterflies, and neuropteroids in the grasslands.

Table 3 lists the top hotspot grid cell for the groups studied in this rarity and richness analysis. Shown is the number of taxa present in this cell compared with the total number plotted. Only three cells are involved, namely, 82E.003, 82E.013, and 83E.053, all in the South Okanagan; cell 82E.003 in the extreme south near Osoyoos dominates. All have low-elevation native grassland as the predominant habitat.

Conclusions

Only a few terrestrial arthropod taxa are involved in this analysis because these are the only taxa to date for which there is an extensive georeferenced distributional, computerized database. When data for other taxa become available, additional analyses will show whether similar results occur.

An examination of Figs. 7–9 shows that collection records are concentrated in the southern part of the province and that those in the northern half are centred on main roads and highways. L.D. Warman and G.G.E. Scudder (unpublished) found that 95% of the records for butterflies in the province are within 3 km of a major road. However, much of the northern half and western third of the province is mountainous and inaccessible. The forested areas in these high, inaccessible areas may not contain suitable habitat for the taxa studied.

Table 3. Top hotspot grid cell, followed by number of taxa found within grid cell and total number of taxa plotted for each group.

Top Hotspot Total No. of Taxa

Plotted

Percentage in Top

HotspotGrid Cell No. of Taxa

Rarity Hotspots

Arthropods 082E.003 130 669 19

Heteroptera 082E.003 37 99 37

Butterflies1 082E.003 12 60 20

Neuropteroids 082E.013 6 18 33

Richness Hotspots

Heteroptera 082E.003 302 623 48

Butterflies 082E.003 97 187 52

Neuropteroids 082E.053 31 74 42

1 See Table 1 for note on taxa included.

130 G. G. E. Scudder

Fig. 10. Top 5% of richness hotspots for the terrestrial Heteroptera.

Fig. 11. Top 5% of richness hotspots for the butterflies.

Grasslands: Biodiversity Hotspots for Some Arthropods in British Columbia 131

Positive relationships found between the species richness of two or more groups may reflect patterns of sampling effort (Gaston 2000). Unfortunately, the collecting effort cannot be assessed in a way that has been used in similar analyses elsewhere (Prendergast, Wood et al. 1993). Nevertheless, main roads and highways in the province pass through all 16 Biogeoclimatic Ecosystem Classification zones, and records show that all of these zones have been sampled.

The results for butterflies reported herein are consistent with the results presented by Kerr (2001) in an analysis of patterns of butterfly species richness in Canada. This is not surprising, because Kerr used the same basic database as is examined herein and did not rely on range maps, as has been done in similar studies in Canada (Warman et al. 2004). Kerr (2001) found that butterfly richness in Canada was correlated with average annual potential evapotranspiration, but the mapping scale used by Kerr was different to that used in the present study.

Although scale can influence the results in such richness analyses (Willis and Whittaker 2002), the analysis used in the present study was based on an Albers Equal Area projection and 1:20,000 scales, which gave 7,056 grid cells in the province, with these grid cells varying from 124.52 km2 in the northeast to 165.16 km2 in the southwest. This is a finer scale than that used by Kerr (2001).

Natural grasslands occupy less than 1% of British Columbia’s land base (Grasslands Conservation Council of British Columbia 2004). Gayton (2004) has pointed out that overgrazing by wild and domestic ungulates, weed invasion, forest ingrowth (encroachment as a result of fire suppression), and habitat fragmentation all threaten the integrity of the

Fig. 12. Top 5% of richness hotspots for the terrestrial neuropteroids.

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grassland ecosystems in the interior of the province. Hence, because these grassland ecosystems are important rarity and richness hotspots for several arthropods and other taxa (Scudder 2005), they are prime areas for biodiversity conservation. The high richness areas detected for the terrestrial arthropods investigated are also high irreplaceability areas for much of the biota in the province (Warman and Scudder 2007). Meir et al. (2004) have concluded that when investment has to be staged over a number of years, the best strategy for biodiversity conservation is probably the protection of sites with the highest species richness or highest irreplaceability.

Furthermore, because grasslands are likely to be the ecosystems that first show response to current climate change (Knapp and Smith 2001), grassland arthropods, which typically have short life cycles, are likely to be among the first biotic elements to demonstrate range change in these high-priority conservation areas. Indeed, many wild animals and plants are already showing the fingerprint of global warming (Parmesan and Yohe 2003; Root et al. 2003). Butterflies in particular are responsive to climate change (Dennis 1993), and elsewhere in the world they show changes in range correlated with climate change (Parmesan 1996; Parmesan et al. 1999; Warren et al. 2001; Wilson et al. 2007). In this context, the butterflies, terrestrial Heteroptera, and terrestrial neuropteroids living in the richness hotspots in British Columbia’s native grasslands warrant conservation, monitoring, and further study.

Acknowledgements

Research for this chapter was supported by grants from the Natural Sciences and Engineering Research Council of Canada and funds from the British Columbia Ministry of Water, Land and Air Protection (now Ministry of Environment). Dr. P. Williams (Natural History Museum, London) kindly provided the WORLDMAP software and custom modified it for application in British Columbia. Richard Doucette (Grasslands Conservation Council of BC) provided an ArcView shape file for the Peace River grasslands area. I thank Annabelle Jessop (Agriculture and Agri-Food Canada, Ottawa), C.S. Guppy, J. Heron, and N. Kondla for providing the butterfly data used in this analysis. I am indebted to Launi Lucas for the preparation and maintenance of the georeferenced distributional databases, for carrying out the mapping, and for help in preparation of the figures and manuscript.

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