BCB 322: Landscape Ecology

1. BCB 322:Landscape Ecology Lecture 7: Emerging patterns II Ecotones

2. Ecotones • First described in 1905 by Clements as “tension zones” where principal species from adjacent communities meet their limits (Farina, 1998) • Importance further stressed by Odum (1959) as transition zones between two communities. • Situated where there is a change in the nature of ecological transfers compared with patch interiors (Farina, 1998) • Basically, ecotones have species in common with both adjacent interior communities, as well as edge-specialist species • Tends to have higher diversity than surrounding areas, and consequently may be interpreted as a habitat in itself (frontier habitat) (Ricklefs, 1973)

3. http://www.geography4kids.com/misc/photos/ecotone.jpg Importance • Provide landscape functions: seeds & animals move across them. & they act as indicators of climatic shift • High biological diversity, and can act as refugia for species under changing conditions (climate/human impacts) • High rate of primary & secondary production, & contribute to system integrity • Riparian, coastal & lacustrine ecotones transmit nutrients & water to aquatic ecosystems & back • Understudied, but provide a good arena for study of natural communities. • Importance realised, & preserved in modern conservation plans where possible

4. Basic concepts • Areas where energy & material exchange are at a maximum in a heterogeneous landscape • In terrestrial systems, they correspond with changes in soil/vegetation, & in heterogeneous systems are situated at patch edges (structural) • May also be functional, & may separate areas of different maturity • Found at all scales, both temporal & spatial • Can be thought of as acting as “cell membranes” or barriers (Forman & Moore, 1992), ensuring active & passive transport between patches. • Previous ecological measures considered archetypal terrain (interiors), but understanding of landscape ecology shows importance of boundaries between regions

5. Difficulty of study • Since they are temporary, and because they scale so broadly, they can be hard to study • Often structure & function not even related to physical patterns, particularly as a result of human activity • Obvious characteristics visible from the air are lost on closer examination • Because it is an edge, it is hard to define the boundaries of an ecotone: some can be fairly short, and others broad even whilst examining at the same spatial scale • Thus edges are generally considered to occur where contrast between patches is greatest (species specific) http://www.class.uidaho.edu/italy2004/ecology_files/ecotone.jpg

6. Species specificity • (a) ants, (b) mammals, (c) lizards (d) birds in a grassland (2700m transect sampled at 30m intervals) • Peaks correspond to discontinuities in resources/ habitats (pairwise sampling) Turner et al. 1990

7. Heirarchical structure • Spatial: • Biome (blending of patches of different shapes & sizes from adjacent biomes) • Environmental mosaic (within biome: the shape & size of internal patches) • Patch (transition between patches) • Population (for species with patchy distribution/ territory) • Individual (eg: tree with localised water conditions or allellopathy) • Temporal: • 104 years: climatic shift changes species distributions • 103 years: historical movement of human civilizations • 102 years: coastal/river dynamics • 10 years: flooding regimes • Seasonal: snowmelt & water availability

8. http://thegreencuttingboard.blogspot.com/Arundo-donax.jpg Controlling factors • Controls may be external or internal • External include edaphic, microclimate, human disturbance • Intrinsic can be species-specific or more broad-based • Allelopathy: pines/eucalypts secrete phenolic inhibitors into the soil, & mosses lower pH (to 3!) of water in contact with them to limit invasion of other species • Reproductive aggressiveness may limit seeding of other plants (Arundo donax, Phragmites, communis) • Sediment capture from wind (dune areas) or water (riparian) by certain species, after microbial intervention, can change nutrient cycles • Animal activity (grazing, digging, seed predation, forest clearance) play a role (eg: tree destruction by elephants creates shrubby ecotones) • Most internal factors still driven by external (moss may change pH, but external conditions must still favour its growth initially)

9. Character of ecotone • (a) gradual - common in nature, such as transition from grassland to woodland • (b) discontinuous – common where a species reaches tolerance limit (such as with salinity, temperature, soil pollutants, water levels) or biological competition • (c) hysteretic – occurs where there is some degree of latency in the system Shugart, 1990 • (d) multiple responses – common where other characters are also relevant, or where there is a complex evolutionary/historical relationship

10. Permeability • Ecotones are important for movement of both animal species & materials/energy (such as resources moved by ants from one patch to another • Permeability: a measure of the capacity of an ecotone to deflect movement of a vector (Wiens et al, 1985) • Differs with vector strength (wind, water), and material will be deposited where kinetic drop is greater Wiens, 1992 • Topography affects dimension of the energy/material fluxes through an ecotone due to kinetic energy & surface:volume ratio • Eg: beaver dams have a high s:v ratio, increasing changes at borders. Also, reduced kinetic energy results in deposition of sediment • High contrast between patches causes true impermeable barriers (common in human-induced areas, rare in nature)

11. Animal movement • Movement across ecotones is non-random & complex • Depends on: • Passive diffusion: depends on patch character, diffusion rate & heterogeneity • Active diffusion: active movement, dependent on movement rate & type, organism density in patch & habitat preferences • Probability of edge encounter: Animals may not encounter ecotones – depends on arrangement, shape & size • Decision to cross: can be modelled as a cost-benefit analysis given species-specific predation & resource constraints • Permeability tends to increase with increasing animal body size. http://home.earthlink.net/~gastropod/bvrdm.JPG

12. Role in landscape • Modify type, extent & direction of movements between landscape components • (eg: riverine woodland increases field stability for agriculture, whilst at the same time providing habitat for the insects that feed on crops) • Reduce negative impacts of wind & some disturbances on patches, & modify soil & temperature character • Edge effects generally increase biodiversity (not for all species), and so may act as refugia for species. • (eg: amphibians tend to live in ecotones, spend their lives in terrestrial habitats, but move to ponds to breed • Likewise, birds may roost in forest but feed in ecotones. • Often possible to predict overall biodiversity by examining ecotone density. • Greatest biodiversity occurs with optimal blend of patches & ecotones

13. Ecotone density Naiman et al., 1988

14. Climate change • Since ecotones may be edges of species tolerances, range shifts can be observed here first • Ecotones used to study vegetation shift (Delcourt & Delcourt, 1987) • Ecotones have differing fragility: mountain ecotones may show change first • Increasing temperatures will dry soils. Although many species can adapt their ecophysiology, broad scale changes will result • Biome-level ecotones will experience reduced biodiversity http://www.aphasiahelp.org/ourpages/brett/images/kokerboom_quivertree.jpg • The quiver tree (Aloe dichotoma) is dying on the northern extremes of its range, and advancing on the southern ecotone (Midgely et al., 2005)

15. Economics • Historically settlement is associated with ecotones (lakes, river deltas, sea coasts) (Desaigues, 1990) • Productivity of a system is assured by ecotones • Removing ecotones was useful (lagoons, marshes, woodland matrices) because it made land available, but has long term effects in breaking nutrient/water cycles • Eg: removal of riparian forest increases water eutrophication as well as the chance of floods • Hedges in Britain acted as windbreaks and changed microclimate of soil, but agriculture intensification has caused their removal • Large ecotones (marshes & river meanders) are too expensive to recover • Hence it is important to preserve these systems to act as functional entities & biodiversity refugia

16. Summary • Transition zones between adjacent systems, with characters defined by scale & interactions between these zones • Situated where rate & dimension of ecological transfers changes • Found at all spatial (biome to individual) & temporal (millennia – daily) scales • Hard to study because patterns vanish under close examination • Selectively permeable to organisms and abiotic factors • Play a vital role in human-disturbed landscapes for biodiversity maintenance • Display changes in climatic conditions because species exist at the edge of their ranges • Zones in which human activity developed are economically useful structures

17. References • Clements, F.C. (1905) Research methods in ecology. University Publishing Co. Lincoln, Nebraska, USA • Desaigues, B. (1990) The socio-economic value of ecotones. In: Naiman, R.J. & Decamps, H. (eds). The ecology and management of aquatic-terrestrial ecotones. MAB, UNESCO, Paris • Farina, A. (1998) Principles and Methods in Landscape Ecology. Chapman & Hall, London, UK • Forman, R.T.T. & Moore, P.N. (1992) Theoretical foundations for understanding boundaries in landscape mosaics. In: Hansen, A.J. a& di Castri, F. (eds). Landscape boundaries. Consequences for biotic diversity and ecological flows. Springer-Verlag, New York • Midgley, G.M., Hughes, G., Thuiller, W., Drew, G. & Foden, W. (2005)Assessment of potential climate change impacts on Namibia’s floristic diversity, ecosystem structure and function. SANBI, Cape Town, UK • Naiman, R.J., Holland, M.M., Decamps, H. & Risser, P.G. (1988) A new UNESCO program: research and management of land:inland water ecotones. Biology International, Special Issue 17: 107-136 • Odum, E.P. (1959) Fundamentals of ecology, 2nd editions. W.B.Saunders Company, Philadelphia • Ricklefs, R.E. (1973) Ecology. Chiron Press • Shugart, H.H. (1990) Ecological models and the ecotones. In: Naiman, R.J. & Decamps, H. (eds). The ecology and management of aquatic-terrestrial ecotones. MAB, UNESCO, Paris, • Turner, S.R., O’Neill, R.V., Conley, W., Conley, M., & Humphries, H. (1990 ) Pattern and scale: statistics for landscape ecology. In: Turner, M.G. and Garnder, R.H. (eds). Quantitative methods in landscape ecology: the analysis and interpretation of landscape heterogeneity. Springer-Verlag, New York • Wiens, J.A., Crawford, C.S. & Gosz, R. (1985) Boundary dynamics: a conceptual framework for studying landscape ecosystems. Oikkos45: 421-427