Ecology MT

Ecology MT

1. Habitat fragmentation & conservation at the landscape scale

   • Habitat loss can cause extinctions via...
     • Species-area relationships
     • Small populations
       • Environmental stoachsticity
       • Demographic stochasticity
       • Allee effects
     • Island biogeography
   • Habitat fragmentation = increase in patchiness
     • Edge effects
     • Subdivision
     • Demographic consequences
       • 1. Extinction  2. Patchy populations 3. The rescue effect 4. Source-sink dynamics 5. Metapopulation dynamics
   • Ecosystem functioning & ecosystem services
   • The Lawton Review

2. Selection & design of protected areas

   • Some biomes underrepresented in protected areas
     • Can be assessed in terms of representativeness & persistence
   • How to select areas to protect
     • Select places where species richness highest
     • Select places where threatened species occur
     • Prioritise areas which have unique sets of species not protected elsewhere
   • Two main goals of reserve design: maximise diversity & minimise extinction
     • Species-area curves: richness increases with area
     • Equilibrium number of species depends on area & isolation
   • SLOSS: a single big reserve is better than a single small reserve but should we have a Single Large reserve Or Several Small reserves with same total area?
     • For Single Large: Lower extinction risks Large-bodied species need large home ranges Against Single Large: Stochastic events Disease May have lower total species richness Evidence: small islands collectively can have more species than a smaller number of large islands with the same area (higher z value)   
   • Habitat corridors
   • Problems with 'rules' for reserve design
     • Theory & rules concerned with maximising diversity – in practice, reserves more likely to be designed with particular threatened species in mind    Conservation in real world is opportunistic – difficult to apply many of rules in practice e.g. purchasing land for round reserve Reserves aren't only way of conserving species – reconciling economic activity & conservation People need to be integrated into reserve designs → biosphere reserves – zonation of land uses (protected area is at core)
     • Protection is not always effective: 'paper parks'

3. Conservation beyond protected areas

   • Approaches for reconciling human activity with biodiversity conservation
     • Sustainable harvesting
     • Wildlife-friendly agricultural practices e.g. agri-environment schemes, agroforestry & valuation
       • Land sparing vs land sharing
       • Do agri-environment schemes help?
         • Despite major investments in agri-environment schemes across Europe over the past ~25 years, populations of farmland birds have continued to decline Efficacy of AESs often judged by trends such as this, but tests for effectiveness of management often carried out at much smaller scales Overall, there is little evidence that European agri-environment schemes are halting declines in farmland biodiversity But: this may be because the schemes are not sufficiently targeted Evidence-based approaches to habitat creation on intensively managed farmland in England can achieve large increases in plant, bee & bird species   
   • Approaches for restoring biodiversity in the wider countryside
     • Reintroductions
       • Red kite: success, no resistance
       • White-tailed sea eagle: controversial
     • Rewilding
     • Restoration ecology
       • An intentional activity that initiates or accelerates the recovery of an ecosystem with respect to its health, integrity & sustainability

4. Agroecology

   • Application of ecological understanding & principles to agriculture  OR  Study of ecological processes that operate in agricultural production systems
   • Agricultural intensification = consequences
   • Organic farming - better for biodiversity & ecosystem services?
     • Organic farms had 30% higher species richness than conventional farms But results were variable: 16% of studies showed a negative effect of organic farming on species richness Positive effect of organic farming was largest in studies performed at a small (plot) scale At the larger (farm) scale the effect was significant but highly variable Organic plots have more diverse microbial communities → correlated with more efficient functioning Biomass & abundance of earthworms were higher by a factor of 1.3 to 3.2 in organic plots → break up soil
   • Heterogeneity matters
     • Loss of ecological heterogeneity is a universal consequence of agricultural intensification Heterogeneity rather than e.g. organic management per se is typically the best predictor of biodiversity outcomes Future policy and management should aim to recreate heterogeneity as the best way of restoring and sustaining biodiversity in temperate agricultural systems Increasing crop heterogeneity can be an effective way to mitigate the impacts of farming on biodiversity without taking land out of production   

5. Ecological & evolutionary processes

   • Methodologies for determining long-term ecological processes
     • 1. Satellite imagery (we have images from 120 years ago in Harvard forest) 2. Historical records 3. Fossil pollen & plant macrofossils 4. Diatoms, chironomids, phytoliths 5. Stable isotopes (δ13C, δ15N, δ18O) 6. Sediment geochemistry e.g. extracting sedimentary cores from peat bogs in the Galapagos islands/frozen lakes in Hungary 7. Mineral magnetics 8. Micro & macrofossil charcoal analysis   
   • Aspects of biodiversity conservation that require an understanding of long-term ecological processes
     • Determining biodiversity baselines & natural variability
       • Sierra de Manatlan UNESCO biosphere reserve
       • Decline of pelagic sharks in Gulf of Mexico
     • Predicting ecosystem thresholds
       • Resilience
         • 1. The capacity of a system to undergo disturbance & maintain its functions & controls 2. Speed of return to an equilibrium following a perturbation from that state
       • Madagascar's littoral forest
       • Disturbance to tropical rainforests
     • Restoration of biodiversity
       • Open land habitats of coastal New England

6. Rewilding

   • The return of habitats to a natural state  Objective: restore trophic structures & missing ecological & evolutionary processes provided by large herbivores
   • Ecological processes associated with large vertebrates
     • 1. Promotion of large, long-lived species over persistent pest & weed assemblages 2. Restoration functionality in ecosystems (e.g. nutrient cycling, seed dispersal) 3. Disturbance regimes leading to increased biomass & overall levels of biodiversity 
   • European rewilding model
     • Classic theory:  Postglacial forest consisted of... - Closed canopy broad-leaved forest (Tilia) & understorey with range of shrubs - Regeneration by means of small/large gaps caused by natural disturbance - Large verts within this forest considered 'forest-dwellers' Alternative theory (Vera, 2000, 2008):  - Large herbivores not passive but essential to ecosystem form & function - Natural vegetation of temperate Europe not closed canopy forest rather a wood-pasture ecosystem - Oak & hazel on early Holocene European landscapes indicative of this - open landscape trees PASSIVE or ACTIVE? - Compare vegetation record between Britain (large herbivores present) & Ireland (mostly not)  - Compared proportion of oak & hazel in forests 9500-6500 yrs ago - Found no distinction = minimal impact?? - Problems with test...
   • North American rewilding model
     • - Usually 1492 AD (arrival of Columbus) suggested as restoration baseline for North America but argue this is 'too late' - Should restore to Late Pleistocene (before of arrival of Americans from Eurasia) 13,000 yr BP & before associated megafaunal mass extinction   
   • Eurasian rewilding model
     • - Currently landscape covered by tundra –when this melts releases large amounts of CH4 into atmosphere - By restoring large grazing animals on the modern tundra will remove the mosses/tundra plants that currently keep the soil moist  - This will recreate extensive grasslands - dramatically reducing greenhouse gas emissions- Pleistocene park established in Siberia, Republic of Yakutia: reconstituted ecosystem  
   • Advantages & disadvantages
   • Tortoises as a restoration tool to replace extinct ecosystem engineers in Mascarene Islands
   • Giant tortoises & wetland biodiversity in the Galapagos islands

7. Fire in savanna ecosystems

   • Fire is a selection pressure - a chemical grazer
   • Brazilian cerrado biome
   • Raunkiaer's life forms
     • - Phanerophyte: buds held at different points in plant - Chamaephyte: buds held close to ground  - Hemicryptophyte: almost at ground level, some below- Geophyte: well below ground, bulbs & rhizomes - Can protect their buds to give increased flowers & seeds - Can sacrifice everything apart from the dark parts to survive to next generation- Habit variation seen in Jacaranda (Bignoniaceae)
   • Ecological effects of fire
     • - Increase soil temperature (only surface layer) -  Remove living biomass and litter- Increase light at soil surface- Ash decreases surface reflectivity – warm soil surface → promotes seed germination - Increase wind and water erosion (wind especially in dry season)- Soil moisture reduced (removes humus from soil) – lack of litter insulation & high transpiration rates- Nutrient loss (N, S) by volatilisation and as dust- Mineralisation and N fixation increase (legumes take advantage) – increase soil pH, Ca, Mg and K  

8. Conservation genetics

   • Working out genetic diversity: richness & evenness
     • - Richness: number of different things, in a sample of fixed size e.g. mean no. of alleles per locus (total no. of alleles divided by no. of loci sampled)  - Evenness: related to distribution of frequencies 
   • HT is the expected gene diversity of all subpopulations when pooled
     • HT is the expected gene diversity in a panmictic (random mating) subpopulation
       • FST = fixation index - differentiation measure for conservation genetics

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