BCB 322: Landscape Ecology

1. BCB 322:Landscape Ecology Lecture 5: Emerging processes II Fragmentation & connectivity

2. Introduction • A core issue for modern conservation planning & landscape ecology (Saunders et al, 1991) • Has been identified as one of the biggest challenges to biodiversity • Proceeds extremely rapidly – in large parts of the world almost all fragmentation occurred in the last century (Australia, Amazonia) • Negative impact on many species due to geographical isolation and sundering of metapopulation communication • Interior species affected more than others Deforestation & development, Tanzania

3. Introduction • Large predators die out first, causing population overruns of other species • These species may then cause further degradation • (eg): removal of the top predator in Zimbabwean national parks (man) led to overpopulation and habitat trashing by elephants • Although island biogeography is used to describe them, fragments are not true islands. • Connectivity & ecotones must also be considered when studying landscape fragmentation • In fact, since all landscapes are inherently patchy, fragmentation may be considered as filling a continuum from untouched wilderness to fully- fragmented • Fragmentation is scale specific for different organisms

4. Scale dependence • If a large area is fragmented into smaller intact areas, it is termed “geographical fragmentation” (coarse-grained) Wiens, 1994 • Fragmentation on the scale of plots is extremely fine-grained (eg): native vegetation in a matrix of invaders • Effects tend to be species-specific due to scale & resource considerations • Specialists are generally worse affected by fine grain fragmentation than generalists • Fragments tend to be more vulnerable to external disturbance (wind, drought, disease)

5. Diversity in fragments • Species assemblages in fragments are usually subsets of those of larger plots • Species assemblages in smaller woodlots tend to be lower than in large ones • Fragmentation method, habitat type and surrounding matrix effect all play a role in the effect of fragmentation on species • Temperate forest birds show high resilience to fragmentation into woodlots • Tropical deforestation immediately reduces biodiversity, and separations of as little as 80m can act as barriers for insects, small mammals & understorey birds • Burning in Chilean forests promotes the growth of Vismia around remnants, whilst logging does not. Remnants surrounded by this species are considered more isolated by birds (Stouffer & Bieregaard, 1995)

6. Fragmentation: species response • Some species suffer more from fragmentation due to habitat size sensitivity (large predators & interior species) • Eg: amphipods in Australian eucalyptus forest showed marked reductions in populations after fragmentation (Margules et al, 1994) • By contrast, scorpions showed no significant change in the same plots, possibly because it is capable of fossorial behaviour. • Small beetles often consider fairly small open spaces to be impassable due to increased risk of dessication • Conservation responses should therefore look at individual species responses and not just α-diversity

7. Fragmentation: species responses • Forest tent caterpillar (Malacostoma disstria) outbreak durations are related to the extent of forest edge/km: parasites & predators are less efficient at the edges (Roland, 1993) • In a study by Kattan et al (1994), showed that between 1959 & 1990, 31% of avifauna in the upland forest of Colombia were eliminated Roland, 1993 • Species that fed in the understorey, and those that required large canopies for fruit provision were hit worse than other species. • Clearly, the effect of fragmentation depends on the biogeography of the species in question

8. Fragmentation & predation Wilcove, 1985 • Species in fragments are often more vulnerable to predation (Wilcove, 1985) • Many other factors affect predation rates at the local level, including vegetation type & cover of the surrounding matrix, • In a fragmentation gradient in Southwestern California, avian nest predators were found to increase with fragmentation, whilst snakes decreased. • Hence, primarily snake-predated species were less impacted by predators in fragments than other species (Patten & Bolger, 2003) http://www.rfadventures.com/images/Animals/Reptiles/Snakes/Non%20Ven/

9. Fragmentation measurement • There are many measures useable for fragmentation, and often severable variables must be combined by regression • Area (& ratios of area: long axis length; area: perimeter) • Structure • Isolation • Surrounding land use • Edges (external & internal) per km • Species turnover in a fragment is calculated as: where E= extinctions C = colonisations S1 & S2 = # breeding species in years 1 & 2 (Diamond, 1969) • Turnover is inversely related to area, with plots over a certain size having a constant turnover rate.

10. Connectedness • Isolation obviously causes problems for species movement. • Three measures of patch isolation can be considered: • connectedness: the degree of physical connection between patches (structural attribute). Obviously, the matrix is the most connected element, but generally connectedness is a measure of the patch structure • connectivity: extent to which subpopulations are connected into a functional demographic unit (functional attribute). • corridors: functional or structural connection between different subpopulation.

11. Connectivity Farina,1998

12. Corridors • Functional structures in a landscape which are fundamental for mitigation of the effects of fragmentation (also for invasive species penetration) • Important concept for conservation planning, to allow movement of organisms through the reserve and surrounds • Consequently, they may be structurally recognisable (such as hedgerows in a field matrix), but are not necessarily so • In fact, there’s little evidence that animals use hedgerows/fencelines as corridors • Many plant species soil conditions for growth & seed conditions that are not guaranteed by a narrow strip of vegetation • Hence, “corridor” is an unclear concept, and is used in different contexts in different places in the literature.

13. Corridors • Can be created by topography (mountain ridges), hydrology (riverbeds) or human forest clearance and other disturbances • Rivers are the best studied corridor structures – often associated with alien invasion due to the patchiness of the riparian structure • Patchiness due to flooding, temporary ponds, seasonal dryness. • Invasibility differs according to hyrdological & geomorphological zones in the river • Furthermore, alien plant invasion can be mitigated due to high seasonal variation www.in.gov/dnr/public/novdec02/corridor.jpg

14. Corridors http://www.dsbn.edu.on.ca/Schools/MarthaC/cougar%2082.jpg • Vital for large home range mammals in human-impacted landscapes (eg: cougar - Felix concolor – can travel up to 5 miles/night (Beier, 1993) • Satellite telemetry is useful for measuring ranges of such species • Telemetry measurements of leatherback turtles showed they followed the same route every year to beaches on Costa Rica (Morreale et al, 1996) • In fact, it appears many species follow “marine corridors” & without testing, these can easily be disrupted by human activity such as fishing • Corridor width plays a role in the viability of a corridor – too narrow and dispersal capacity is limited

15. Summary • Fragmentation is a global process that reduces biodiversity & accelerates local & global extinctions • Fragmentation increases habitat edges and the potential for predation • Fragmentation is a species specific measure, and although one species may see the environment as fragmented, it may be homogeneous for another • Animal dispersion/movements increase with fragmentation • Connectivity is a functional measure of fragmentation • Connectedness is the structural corollary to connectivity • Corridors are essential for the maintenance of biodiversity in a fragmented landscape, although definitions of corridors vary

16. References • Diamond, J.M. (1969) Avifaunal equilibria and species turnover rates on the Channel Islands of California. Proceedings of the National Academy of Sciences, USA69:3199-3203 • Farina, A. (1998) Principles and Methods in Landscape Ecology. Chapman and Hall, London, UK • Kattan, G.H., Alvarez-Lopez & H., Giraldo, M.(1994) Forest fragment and bird extinctions: San Antonio eighty years later. Conservation Biology8: 138-146 • Margules, C.R., Gaston, A.J. & Hitier, S. (1994) Contrasting effects of habitat fragmentation on the scorpion Cercophonius squama and an amphipod.Ecology75: 2033-2042 • Patten, M. A. and Bolger, D. T. 2003. Variation in top-down control of avian reproductive success across a fragmentation gradient. – Oikos 101: 479–488. • Roland, J. (1993) Large-scale forest fragmentation increases the duration of tent caterpillar outbreak. Oecologia93: 25-30 • Saunders, D.A., Hobbs, R.J. & Margules, C.R. (1991) Biological consequences of ecosystem fragmentation: a review. Conservation Biology 5: 18-32 • Stouffer, P.C. & Bierregaard, R.O. (1995) Use of amazonian forest fragments by understory insectivorous birds. Ecology76: 2429-2445 • Wiens, J.A. (1994) Habitat fragmentation: island v landscape perspectives on bird conservation. Ibis137: S97-S104 • Wilcove, D.S. (1985) Nest predation in forest tracts and the decline of migratory songbirds. Ecology66:1211-1214