Lecture 19 Dynamic Biogeography

Species Patterns (3)

1. Historical factors determine regional pool of species

• evolution, climate change, catastrophes like asteroid impact

2. Abiotic factors govern distribution and abundance within the region

• time from origin, pH, rainfall, site fertility, disturbance, distance from regional species pool (e.g. island biogeography)

3. Biotic factors further govern distribution and abundance within the community

• dispersal, species interaction, community structure

Changes in species patterns

• historical processes affecting present patterns

  • e.g. Pleistocene biogeographic dynamics

• future patterns: the possible impacts of change during 21stC

  • impacts of climate change

  • human impacts

Pleistocene and Holocene (9)

• the past two million years -> but what came before?

• tectonic movements affecting climate, ocean currents, marine and land life, biotic interactions

  • completely different land distributions in past geological ages

• glacial-interglacial cycles

• movement of entire climatic zones during past periods

• climatic combinations without contemporary analogues

• massive temperature differences from Pleistocene LGM far from glacial edges

• little tectonic movement between periods but significant climatic change

• regionally variable effects

  • jet stream moves

  • shifting of climate patterns, potentially warmer in some areas

  • temperature but also aridity, etc.

• sea level change

Glacial-interglacial cycles

• interglacial periods have made up 10% of the past 2 million years

• glacial periods cooler, wetter in North America, drier in Europe and the tropics e.g.

Impacts of sea level change

• land bridges, marine channels

  • effects on dispersal, speciation, community structure

  • Wallace Line between South East Asia and Oceania

    • first noticed by Venetian explorer Pigafetta

• total amplitude of over 230m during Pleistocene possible

Biogeographic dynamics in the Pleistocene

• Environment

  • location, extent, configuration of habitat

  • changes in nature of climatic zones

  • formation and dissolution of dispersal routes

• Biotic responses

  • move

  • remain: tolerate or adapt

  • reduction in range, eventual extinction (why, if population not completely lost in sudden events? viable size tipping point)

Postglacial biogeographical dynamics (4)

• disjunct species distributions

• shifts can vary

  • mountains, rivers, etc

  • European mountain ranges largely run east-west, blocking north-south migrations

• North American forest types

  • expansions/reduction of forest and tundra long Mississippi river during ‘Wisconsin’ glacial period

• mountains

  • shifts of biomes higher up mountains

  • cooling -> reduced area, extinctions

  • warming -> increased dispersal

What responds to biogeographic shifts (6)

• communities, species, or individuals

• dependent on physiology, behaviour, life history, reproductive capacity, etc.

• combination of species and individuals

• differences within and among species

  • northward expansion of white spruce (Picea glauca), faster dispersal in west because of north-flowing winds

  • individualistic species expansions and contractions, non-analogue communities as well as non-analogue climate/soil combinations

• composition and abundance of biomes varies over time

• glacial-interglacials led to a series of individualistic responses in animals and plants, creating and breaking up ecological relationships

  • reshuffling of communities, influence of refugia

  • reaching an ‘equilibrium’?

Human Influences

• domestication of plants and animals, land use change

• extinction, especially of animas

  • plants: many extinctions 5-0.7 million ybp

  • animals: many large-scale extinctions after LGM, e.g. mega-fauna

  • climate change or human-driven

Predicting responses to 21st Century change

• models of vegetation growth (photosynthesis and respiration)

• use carbon as the currency for success or failure

  • differential success

  • climate

• build models from the bottom up

  • process based not pattern based

Predicted rates of change from IPCC

• boreal zone shifting northward: 5km/year, loss or gain in total area

• temperature zone shifting northward: 5km/year, overall gain in area

• topical mountains shifting upwards: 2-5m/year, overall loss in area

• rates of migration larger than Pleistocene changes

  • 50-3000m/year

  • not completely analogue to Pleistocene shifts

• scenarios of initial losses of biodiversity as species

  • differentially migrate, some with more longevity than others

  • migrate through fragmented (e.g agricultural) landscapes

Modelling the present and future carbon cycle (4+4)

• Approaches

1. Equilibrium climate and biogeographic vegetation models (IPCC 1995: VEMAP group)

2. Specified climate and dynamic vegetation (IPCC 2001)

3. Fully coupled dynamic climate and vegetation models (IPCC 2001)

4. DGVMs that include NBP(net bioproductivity) estimate (e.g. fire frequency) and land use change

• Static ‘equilibrium’ biogeographic models

• Generic dynamic global vegetation model

• models that include land surface/carbon cycle have very different results

• ‘Intermediate’ biogeographic models

Static ‘equilibrium’ biogeographic models (3)

• assuming no secondary (ie. regrowth) vegetation

• Climate, atmosphere and vegetation distribution/type -> new climate, atmosphere and vegetation distribution/type

• no transition, no dynamic responses (e.g. to CO2, water use)

Generic DGVM (2)

• have equations at their root

• e.g. stomatal variation affects evaporation, temperature

GCMs and DGVMs interactively (4)

• running GCM and DGVM interactively, temperatures 2-3C higher than standard scenario with carbon cycle involved

• responses in soil/vegetation and surface-climate interactions

• uncertainty in DGVM and climate model

• recent analysis showing need to improve veg and climate models, Cox et al 2000, Huntingford et al 2013

Intermediate Biogeographic Models (4)

• include idea of migration requirements

• models on local levels

• estimate species richness changes on basis of changes in area

• assumptions of niche requirements

Vulnerability, dynamic change, and recovery

• bistable and multistable systems -> tipping points

• non-linear change past a threshold

• recovery to original state maybe not possible, even if wider climate recovers

• Maslin 2004 % tree cover compared to dry season length