BIO-201 ECOLOGY 2. Community Ecology and Dynamics – Succession and Stability H.J.B. Birks
Community Ecology and Dynamics - Succession and Stability Some ecological and environmental basics Succession Basic concepts Primary succession on glacial forelands Community changes Ecosystem changes Mechanisms of succession Stability Basic concepts What causes resilience? Alternative stable states and regime shifts Maintenance dynamics Disturbance and diversity Community concepts revisited Conclusions and Summary
Pensum The lecture, of course, and the PowerPoint handouts of this lecture on the BIO-201 Student Portal Also ‘Topics to Think About’ on the Student Portal filed under projects
Topics to Think About On the Bio-201 Student Portal filed under Projects, there are several topics to think about for each lecture. These topics are designed to help you check that you have understood the lecture and to identify important topics for discussion in the Bio-201 colloquia. In addition, there are two or three more demanding questions at the sort of level you can expect in the examination question based on my 10 lectures. These can also be discussed in the colloquia.
Background Information There is now a wealth of good or very good ecology textbooks but perhaps no excellent, complete, or perfect textbook of ecology. Not surprising, given just how diverse a subject ecology is in space and time and all their scales. This lecture draws on primary research sources, my own knowledge, experience, observations, and studies, and several textbooks.
Textbooks that provide useful background material for this lecture Begon, M. et al. (2006) Ecology. Blackwell (Chapter 16, 1 in part) Bush, M. (2003) Ecology of a Changing Planet. Prentice Hall (Chapters 15, 16) Krebs, C.J. (2001) Ecology. Benjamin Cummings (Chapter 21) Miller, G.T. (2004) Living in the Environment. Thomson (Chapter 8) Molles, M.C. (2007) Ecology Concepts and Applications. McGraw-Hill (Chapter 20) Ricklefs, R.E. & Miller, G.L. (2000) Ecology. W.H. Freeman (Chapter 28) Smith, R.L. & Smith, T.M. (2007) Ecology and Field Biology. Benjamin Cummings (Chapters 21, 22) Townsend, C.R. et al. (2008) Essentials of Ecology. Blackwell (Chapters 9, 10)
A Reminder If you try to read Begon, Townsend, and Harper (2006) Ecology – From Individuals to Ecosystems, there is a 17-page glossary of the very large (too large!) number of technical words used in the book on the Bio-201 Student Portal. It can be downloaded from the File Storage folder. Good luck!
Some Ecological and Environmental Basics Environment varies continuously in SPACE at all spatial scales (geology, soils, climate, altitude, slope, etc.) and varies at all TIME scales (days, months, seasons, years, decades, centuries, millennia, etc.)
Coastal chaparral and scrub Coniferous forest Desert Coniferous forest Prairie grassland Deciduous forest Appalachian Mountains Mississippi River Valley Great Plains Rocky Mountains Great American Desert Sierra Nevada Mountain Coastal mountain ranges 15,000 ft 10,000 ft Average annual precipitation 5,000 ft 100-125 cm (40-50 in.) 75-100 cm (30-40 in.) 50-75 cm (20-30 in.) 25-50 cm (10-20 in.) below 25 cm (0-10 in.) Broad spatial scale Biomes Role of climate
Long time scales • Change in temperature in the North Sea over the past 65 million years (M yr). • The ancient continent of Gondwanaland began to break up about 150 M yr ago. • ~50 M yr ago distinctive bands of vegetation had developed. • By 32 M yr these are more sharply defined. • By 10 M yr ago much of the present geography of the continents was established but with different climates and vegetation from today: position of Antarctic ice cap is schematic.
Changing continental positions in last 220 million years Tectonic plates in constant motion. Environment on earth changes accordingly. • Triassic 220 million years ago • Pangaea continent had its maximum size. Large interior areas, very dry and extensive deserts. • Mid-Late Jurassic155 million years ago • Beginnings of the break-up of Pangaea.
3. Late Jurassic149 million years ago Break-up of Pangaea, large (100 m) rise in sea-level, Siberia and China now island continents, Europe a series of islands. 4. Early Cretaceous127 million years ago Break-up of Gondwana.
5. Mid Cretaceous106 million years ago Europe still a series of islands, North and South America widely separated. 6. Late Cretaceous65 million years ago Similar to today but for North and South America and India.
Devonian Neoprotoerozoic III Cretaceous Silurian Jurassic Carboniferous Quaternary Cryogenian/Neoproterozoic III Ordovician Palaeogene Late Triassic Permian Triassic Cambrian Cryogenian Cryogenian Neoproterozoic III
At the same time, major changes in plant evolution and hence in earth vegetation
Global ecological changes in the last 55 million years • Eocene55 million years ago • Widespread tropical rain-forest and no ice-caps • Late Eocene35 million years ago • Cooler, less tropical rain-forest, some ice-caps
3. Oligocene25 million years ago Cooler, more extensive Antarctic ice-cap. Semi-arid scrub and desert areas, evolution of giant land mammals 4. Miocene3.2 million years ago Continents almost in today's position, ice-caps at both poles, climate drier, vast grasslands, much mountain uplift
5. Late Pliocene1-2 million years ago Extensive polar ice-caps, much reduced tropical rain-forest 6. Pleistocene30 000 years ago Massive ice-sheets, much tundra and arid vegetation
Shorter time scales Temperature changes in the Northern Hemisphere at different time scales years years 102 105 103 5x105 104
Holocene 11500 years Medieval optimum Last millennium LIA = Little Ice Age LIA End of LIA Past 130 years
Millennium scale: warm period 1000 AD and the Little Ice Age Medieval Warm Period LIA
Biosphere Biosphere Ecosystems Communities Populations Organisms Today’s Ecological Scale Biosphere Biomes Ecosystems & Landscapes COMMUNITIES Species Populations Organisms
Succession – Basic Concepts • Changing plant and animal communities, ecosystems, and landscapes through time following the creation of new substrates or following disturbance, usually directional changes. • Primary succession – occurs on newly formed surfaces such as volcanic lava flows, areas recently deglaciated (glacial forelands), sand-dunes along coast, etc. • Secondary succession – occurs where disturbance destroys a community without destroying the soil. Occurs after agricultural areas are abandoned, after forest fires, forest clearance, erosion, etc.
Successional change is usually directed towards the undisturbed surrounding vegetation and fauna. • Succession generally ends with a mature community whose populations are relatively stable. 'Climax vegetation'. • Environment is changing at a range of scales in time and space, so communities are always in a state of flux and change. • Successional time scales – can be short or long. Few years; 250 years after the Little Ice Age; 10000 – 11500 years since the last glaciation. • Ecological succession “non-seasonal, directional, and continuous pattern of colonisation and extinction on a site by species populations” (Begon et al. 2006 p.479)
Primary succession e.g. New surfaces formed by: Glacier retreatVolcanic eruptionCoastal sand-dunes Lichens and mosses Exposed rocks Balsam fir, paper birch, and white spruce Jack pine, black spruce, and aspen Heath mat Small herbs and shrubs Time
Mature oak-hickory forest Young pine forest Perennial weeds and grasses Shrubs Annual weeds Time Secondary succession e.g. Disturbance by:FireForest cuttingErosion Wind-throw & storms Abandoned fields Large herbivores e.g. elephants
Differences between primary and secondary succession Primary succession: no soil, no seed-bank, no organic matter Secondary succession: soil is present but disturbed, seed bank present, organic matter present Secondary succession is very common within landscapes, primary succession is less common
Primary Succession and Glacial Forelands Little Ice Age at about 1750 AD caused rapid advance of glaciers in, for example, Jostedal and Jotunheimen. As ice subsequently retreated, deposited glacial moraines (silt, sand, gravel) on which primary succession could begin. Some classic studies mentioned in this lecture: Nigardsbreen, Jostedalsbreen - Knut Fægri Storbreen, Jotunheimen - John Matthews Klutlan Glacier, Yukon - John Birks Glacier Bay, Alaska - W. Cooper et al. Surface ages determined by historical observations, from the size of lichen (lav) thalli on rocks on the surface ('lichenometry'), and from annual growth rings of shrubs and trees. Surfaces of different ages form a CHRONOSEQUENCE.
Glacier Moraines Age of formation 1930 1890 1850 1750 soil pH distance from glacier Age Chronosequences – series of sites (e.g. glacier moraine forelands, volcanic lava flows, sand dunes, recently formed islands) of different but known age. Study vegetation and soils today on surfaces of different but known age. Substitute space today for time – "space-for-time" substitution.
Nigardsbreen 'Little Ice Age' moraine chronology Knut Fægri Photo: Bjørn Wold
Primary Succession after Little Ice Age Photo: 1984 1912-30 Mature Betula forest 1815 1770 Mature Betula forest 1750 Mature Alnus forest
Nigardsbreen, Jostedalsbreen 1931 1874 1900 1987
Vegetation changes since ice retreat 20 years 80 years 150 years 220 years
Distribution of selected species on Storbreen moraines ‘Pioneer’ r-selected species ‘Late stage’ K-selected species
Pioneer plants on Moraine II (2-5 yr) (Crepis nana) Dryas drummondii mats (9-25 yr) Moraine II (10-30 yr) Moraine III (30-60 yr)
Moraine IV (60-80 yr) Moraine IV (95-180 yr) Moraine V (180-240 yr) Harris Creek (>250 yr)
Glacier Bay, Alaska • Phases • Pioneer phase – 20 years – Epilobium latifolium, Dryas drummondii, Salix spp. • 30 years - Dryas mats with Alnus crispa, Salix, Populus, and Picea • 40 years – Alnus forms dense thickets • 50-70 years – Picea and Populus grow above Alnus • 75-100 years – Picea forest with mosses • 200 years – Tsuga heterophylla & T. mertensiana forest • >300 years – more open forest with areas of bogs and tundra meadows
Some Glacier Bay pioneer species Dryas drummondii Epilobium latifolium William S. Cooper
1957 Little Ice Age in Nepal about 1850 2002 Little Ice Age maximum O.R. Vetaas
Terminal moraine-complex Neoglacial stages (> 1200 BP) river Little Ice Age maximum (app. 1850) Glacial lake Gangapurna North Nepal stages since 1850 to present Glacier in 1957 1988 Lateral moraine stages Glacier fronts 2001
Other Primary Successions • Coastal fore-dunes