Predation has long been implicated as a major selective force in the evolution of several morphological and behavioral characteristics of animals. The importance of predation during evolutionary ti...

Behavioral decisions made under the risk of predation: a review and prospectus

Riparian zones possess an unusually diverse array of species and environmental processes. The ecological diversity is related to variable flood regimes, geographically unique channel processes, altitudinal climate shifts, and upland influences on the fluvial corridor. The resulting dynamic environment supports a variety of life-history strategies, biogeochemical cycles and rates, and organisms adapted to disturbance regimes over broad spatial and temporal scales. Innovations in riparian zone management have been effective in ameliorating many ecological issues related to land use and environmental quality. Riparian zones play essential roles in water and landscape planning, in restoration of aquatic systems, and in catalyzing institutional and societal cooperation for these efforts.

The Ecology of Interfaces: Riparian Zones

Natural flood plains are among the most biologically productive and diverse ecosystems on earth. Globally, riverine flood plains cover > 2 × 106 km2, however, they are among the most threatened ecosystems. Floodplain degradation is closely linked to the rapid decline in freshwater biodiversity; the main reasons for the latter being habitat alteration, flow and flood control, species invasion and pollution. In Europe and North America, up to 90% of flood plains are already ‘cultivated’ and therefore functionally extinct. In the developing world, the remaining natural flood plains are disappearing at an accelerating rate, primarily as a result of changing hydrology. Up to the 2025 time horizon, the future increase of human population will lead to further degradation of riparian areas, intensification of the hydrological cycle, increase in the discharge of pollutants, and further proliferation of species invasions. In the near future, the most threatened flood plains will be those in south-east Asia, Sahelian Africa and North America. There is an urgent need to preserve existing, intact flood plain rivers as strategic global resources and to begin to restore hydrologic dynamics, sediment transport and riparian vegetation to those rivers that retain some level of ecological integrity. Otherwise, dramatic extinctions of aquatic and riparian species and of ecosystem services are faced within the next few decades.

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Riverine flood plains: present state and future trends

Null models in ecology

Amazon forests are a key but poorly understood component of the global carbon cycle. If, as anticipated, they dry this century, they might accelerate climate change through carbon losses and changed surface energy balances. We used records from multiple long-term monitoring plots across Amazonia to assess forest responses to the intense 2005 drought, a possible analog of future events. Affected forest lost biomass, reversing a large long-term carbon sink, with the greatest impacts observed where the dry season was unusually intense. Relative to pre-2005 conditions, forest subjected to a 100-millimeter increase in water deficit lost 5.3 megagrams of aboveground biomass of carbon per hectare. The drought had a total biomass carbon impact of 1.2 to 1.6 petagrams (1.2 × 1015 to 1.6 × 1015 grams). Amazon forests therefore appear vulnerable to increasing moisture stress, with the potential for large carbon losses to exert feedback on climate change.

/pdf/drought-sensitivity-of-the-amazon-rainforest-1suraidilh.pdf

Drought sensitivity of the Amazon rainforest.

We suggest here that large-scale natural forest disturbance and primary succession in the lowland rainforests of the Peruvian Amazon is caused by lateral erosion and channel changes of meandering rivers. Our results indicate that in the upper Amazon region, primary succession on newly deposited riverine soils is a major mode of forest regeneration. Landsat imagery analyses show that 26.6% of the modern lowland forest has characteristics of recent erosional and depositional activity; 12.0% of the Peruvian lowland forest is in successional stages along rivers. This successional development is used to classify the western Amazon rainforests according to their geomorphological erosion–deposition pattern. We also propose that by causing high site turnover, disturbance and variation in forest structure, the river dynamics may be a major factor creating and maintaining the high between-habitat (β-type) species diversity characterizing the upper Amazon1.

River dynamics and the diversity of Amazon lowland forest

SUMMARY (1) The major proportion of western Amazon forests grow on fluvial deposits and thus originated in floodplain environments. The fluviodynamic character of the sites initially colonized by plants was studied along different river types, and this information was combined with botanical observations from the same areas. Special emphasis was given to colonizing plant distribution and survival in relation to the abiotic environment. (2) Four frequently occurring landform types, each rich in microforms, were recognized in relation to the colonization process: fluvial bars, swales, abandoned channels and riverbanks. They are affected by seasonal fluctuations in the rivers and tend to be narrow, curved or linear patches. Local site and colonizing vegetation characteristics vary considerably between different river types (meandering or braided, rich or poor in suspended sediment). (3) The newly deposited fluvial sediments are poor in organic carbon and nitrogen. Colonization begins either with immigrant propagules dispersed by wind or water, or with the invasion of species by vegetative means. Usually numbers of individuals are few, and the initial vegetation pattern is a reflection of the small-scale mosaic of microsites. The pioneer flora (125 species recorded) includes many widespread perennial herbs, and seeds of most forest species do not germinate in the dry sediments. Herbaceous colonist species are almost non-existent in suspension-poor rivers of low erosion rate. (4) The persistence of the initial plant assemblage is controlled by the evolution of fluvial landforms. Only a few species among the set of colonists are significant in later forest succession. These include Tessaria integrifolia and Gynerium sagittatum, which resist moderate flood damage and resprout after burial. Mature seed populations of these 10- 15-m-tall species are abundant at the outermost margin of the successional forest just beyond the fluvial bars. The low representation of tree species in the colonizing phase suggests that the extreme environmental conditions at the river margins differ from other natural environments along the Amazon. (5) Aquatic succession on lakes affected by suspension-rich waters starts with genuine floating species. The general habits of these vegetation assemblages and their species composition are highly similar in the 'white-water' floodplains of the study area. An annual vegetation flush characteristically follows the flood period. On the other hand, macrophyte vegetation is almost non-existent on the floodplain lakes of suspension-poor rivers.

New site formation and colonizing vegetation in primary succession on the

The major proportion of western Amazon forests grow on fluvial deposits and thus originated in floodplain environments. The fluviodynamic character of the sites initially colonized by plants was studied along different river types, and this information was combined with botanical observations from the same areas. Special emphasis was given to colonizing plant distribution and survival in relation to the abiotic environment. Four frequently occurring landform types, each rich in microforms, were recognized in relation to the colonization process : fluvial bars, swales, abandoned channels and riverbanks (...)

https://www.jstor.org/stable/info/2261087

New site formation and colonizing vegetation in primary succession on the western Amazon floodplains.

Haffer's refuge theory proposes that during the arid climatic phases of the late Pleistocene, tropical lowland forests of Amazonia were reduced to isolated patches contributing to the high species richness of the present-day forest. The theory was developed because no obvious historic or modern geomorphic isolation barriers were recorded in Amazonia. Analyses of radar images combined with stratigraphical data show that in the basinal forelands of the tectonically active Andes the geological setting causes long-term fluvial perturbance. This leads to a temporally structured highly complex mosaic of fossil and present floodplains. These dynamics have been present with varying activity and geographic range during the Tertiary and Quaternary, providing site-turnover that has not been recognized by the biogeographic tradition of the Amazon basin.

http://science.sciencemag.org/content/sci/238/4832/1398.full.pdf

Fluvial perturbance in the Western Amazon basin: regulation by long-term sub-andean tectonics.

Still active Sub-Andean foreland deformation is suggested to have syndepositionally modified the fluvial depositional environments in the Peruvian Amazonian foreland basin throughout Neogene-Quaternary time. Modern fluvial aggradation continues to proceed on a large scale (c. 120 000 km2) in two differing depositional systems. Firstly, various multistoried floodbasin deposits are derived from the meandering and anastomosing rivers within the subsiding intraforeland basins. Secondly, in the northern part of the Pastaza-Maranon basin the largest known Holocene alluvial fan-like formation (c. 60 000 km2) composed of reworked, volcaniclastic debris derived from active Ecuadorian volcanoes, has been identified.The widespread, poorly known, dissected surface alluvium (terra firme) which covers the main part of the Peruvian Amazonian foreland basin shows further evidence of long-term foreland deformation, and terraces indicate both the effects of tectonism and Pleistocene climatic oscillations. In northern Peru, the surface alluvium was deposited by a Tertiary fluvial system with palaeocurrents to the west and northwest into the Andean foreland basin. In southern Peru, the respective surficial alluvium was part of a post-Miocene fluvial system flowing northeast into the main Amazon basin. Both systems were gradually abandoned when the eastward migrating Andean foreland deformation led to the more distinctive partitioning of the intraforeland basins, and the modern drainage system was created.

Jukka Salo

Papers

River dynamics and the diversity of Amazon lowland forest

New site formation and colonizing vegetation in primary succession on the

New site formation and colonizing vegetation in primary succession on the western Amazon floodplains.

Fluvial perturbance in the Western Amazon basin: regulation by long-term sub-andean tectonics.

Recent and ancient fluvial deposition systems in the Amazonian foreland basin, Peru