Abstract
Changes in the composition of biological communities can be elicited by competitive exclusion, wherein a species is excluded from viable habitat by a superior competitor. Yet less is known about the role of environmental change in facilitating or mitigating exclusion in the context of invasive species. In these situations, decline in a native species can be due to the effects of habitat change, or due to direct effects from invasive species themselves. This is summarized by the “driver-passenger” concept of native species loss. We present a multi-year study of tree squirrels that tested the hypothesis that tree canopy fragmentation, often a result of human development, influenced the replacement of native western gray tree squirrels (Sciurus griseus) by non-native eastern gray tree squirrels (Sciurus carolinensis). We tested this hypothesis along a continuum of invasion across three study sites in central California. We found that within the developed areas of the University of California at Santa Cruz campus and city of Santa Cruz, S. carolinensis excluded S. griseus from viable habitat. The competitive advantage of S. carolinensis may be due to morphological and/or behavioral adaptation to terrestrial life in fragmented hardwood forests. We classify S. carolinensis as a “driver” of the decline of native S. griseus in areas with high tree canopy fragmentation. Future habitat fragmentation in western North America may result in similar invasion dynamics between these species. Our study warrants consideration of existing and predicted interactions between potentially invasive species that co-occur with native species where land use change is proposed.
This is a preview of subscription content, log in via an institution to check access.
Similar content being viewed by others
References
Andren H (1994) Effects of habitat fragmentation on birds and mammals in landscapes with different proportions of suitable habitat: a review. Oikos 71:355–366
Bennett A, Thompson M, Strauss S (2011) Multiple mechanisms enable invasive species to suppress native species. J Am Bot 98:1086–1094
Bruemmer C, Lurz P, Larsen K, Gurnell J (2000) Impacts and management of the alien eastern gray squirrel in Great Britain and Italy: lessons for British Columbia. In: Darling LM (ed) Proceedings of the Conference on the Biology and Management of Species and Habitats at Risk. February 15–19, 1999. University College of the Cariboo, Kamloops, British Columbia. Ministry of Environment, Lands and Parks, Victoria, British Columbia
Buckland ST, Anderson DR, Burnham KP, Laake J (1993) Distance sampling: estimating abundance of biological populations. Chapman & Hall, London
Carraway L, Verts B (1994) Sciurus griseus. Mammalian Species 474:1–7
Didham RK, Tylianakis JM, Hutchison MA, Ewers RM, Gemmell NJ (2005) Are invasive species the drivers of ecological change? Trends Ecol Evol 20:470–474
Fahrig L (2000) Effects of habitat fragmentation on biodiversity. Annu Rev Ecol Evol Syst 34:487–515
Fimbel C, Freed S (2008) Monitoring western gray squirrels for landscape management in western Washington. Northwest Sci 82:299–308
Gonzales E, Wiersma Y, Maher A, Nudds T (2008) Positive relationship between non-native and native squirrels in an urban landscape. Can J Zool 86:1–8
Grarock K, Tidemann CR, Wood J (2013) Are invasive species drivers of native species decline or passengers of habitat modification? A case study of the impact of the common myna (Acridotheres tristis) on Australian bird species. Austral Ecol 39:106–114
Gurnell J (1987) The natural history of squirrels. Christopher Helm, London
Gurnell J, Wauters L, Lurz P, Tosi G (2004) Alien species and interspecific competition: effects of introduced eastern grey squirrels on red squirrel population dynamics. J Anim Ecol 73:26–35
Haff T, Brown M, Tyler W (2008) The Natural History of the UC Santa Cruz Campus, 2nd edn. University of California, Santa Cruz
Hall ER (1981) The mammals of North America, 2nd edn. Wiley, New York
Hardin G (1961) The competitive exclusion principle. Science 131:1292–1297
Holway D (1999) Competitive mechanisms underlying the displacement of native ants by the invasive Argentine ant. Ecology 80:238–251
Johnston AN (2013) Eastern gray squirrel ecology and interactions with western gray squirrels. PhD Dissertation, University of Washington
Koprowski J (1994) Sciurus carolinensis. Mammalian Species 480:1–9
Laurance WF, Lovejoy TE, Vasconcelos HL, Bruna EM, Didham RK et al (2002) Ecosystem decay of Amazonian forest fragments: a 22-year investigation. Conserv Biol 16:605–618
Lawes R, Grice A (2010) War of the weeds: competition hierarchies in invasive species. Austral Ecol 8:871–878
Linders MJ, Stinson DW (2007) Washington state recovery plan for the western gray Squirrel. Washington Department of Fish and Wildlife, Olympia
MacDougall AS, Turkington R (2005) Are invasive species the drivers or passengers of change in degraded ecosystems? Ecology 86:42–55
Mack R, Simberloff D, Lonsdale W, Evans H, Clout M, Bazzaz F (2000) Biotic invasions: causes, epidemiology, global consequences, and control. Ecol Appl 10:689–710
Reynolds J (1985) Details of the geographic replacement of the red squirrel (Sciurus vulgaris) by the grey squirrel (Sciurus carolinensis) in eastern England. J Anim Ecol 54:149–162
Sakai AK, Allendorf FW, Holt JS, Lodge DM, Molofsky J, With KA, Baughman S, Cabin RJ, Cohen JE, Ellstrand NC, McCauley DE, O’Neil P, Parker IM, Thompson JN, Weller SG (2001) The population biology of invasive species. Annu Rev Ecol Syst 32:305–332
Saunders D, Hobbs R, Margules C (1991) Biological consequences of ecosystem fragmentation: a review. Conserv Biol 5:18–32
Skelcher G (1997) The ecological replacement of red by grey squirrels. In: Gurnell J, Lurz P (eds) The conservation of red squirrels, Sciurus vulgaris L. PTES, London, pp 67–78
Steele MA, Koprowski JL (2001) North american tree squirrels. Smithsonian Institution Press, Washington, D.C., p 201
Thomas J (1961) Flora of the Santa Cruz Mountains: a manual of the vascular plants. Stanford University Press, Stanford
Vila M, Weiner J (2004) Are invasive plant species better competitors than native plant species? Evidence from pairwise experiments. Oikos 105:229–238
Vincent JP, Gaillard JM, Bideau E (1991) Kilometric index as biological indicator for monitoring forest roe deer populations. Acta Theriol 36:315–328
Wauters L, Lurz P, Gurnell J (2000) The interspecific effects of grey squirrels (Sciurus carolinensis) on the space use and population demography of red squirrels (S. vulgaris) in conifer plantations. Ecol Res 15:271–284
Wauters L, Gurnell J, Martinoli A, Tosi G (2002a) Interspecific competition between native Eurasian red squirrels and alien grey squirrels: does resource partitioning occur? Behav Ecol Sociobiol 52:332–341
Wauters LA, Tosi G, Gurnell J (2002b) Interspecific competition in tree squirrels: do introduced grey squirrels (Sciurus carolinensis) deplete tree seeds hoarded by red squirrels (S. vulgaris)? Behav Ecol Sociobiol 51:360–367
With KA (2004) Assessing the risk of invasive spread in fragmented landscapes. Risk Anal 24:803–815
Acknowledgements
We thank the James Stuart Chanley Memorial Foundation for providing funds for this study. We also thank Gage Dayton and Alex Jones of the UC Natural Reserve System and Chris Lay, curator of the UCSC Museum of Natural History, for their generous input throughout the study. Gratitude is also due to the numerous graduate and undergraduate students, including the UCSC Small Mammal Research Team, who contributed to the field work. Finally, we thank Rianne Diepstraten and two anonymous reviewers for their thoughtful comments and edits.
Author information
Authors and Affiliations
Corresponding author
Rights and permissions
About this article
Cite this article
Jessen, T., Wang, Y. & Wilmers, C.C. Habitat fragmentation provides a competitive advantage to an invasive tree squirrel, Sciurus carolinensis . Biol Invasions 20, 607–618 (2018). https://doi.org/10.1007/s10530-017-1560-8
Received:
Accepted:
Published:
Issue Date:
DOI: https://doi.org/10.1007/s10530-017-1560-8