438 research outputs found
Comparing process-based and constraint-based approaches for modeling macroecological patterns
Ecological patterns arise from the interplay of many different processes, and
yet the emergence of consistent phenomena across a diverse range of ecological
systems suggests that many patterns may in part be determined by statistical or
numerical constraints. Differentiating the extent to which patterns in a given
system are determined statistically, and where it requires explicit ecological
processes, has been difficult. We tackled this challenge by directly comparing
models from a constraint-based theory, the Maximum Entropy Theory of Ecology
(METE) and models from a process-based theory, the size-structured neutral
theory (SSNT). Models from both theories were capable of characterizing the
distribution of individuals among species and the distribution of body size
among individuals across 76 forest communities. However, the SSNT models
consistently yielded higher overall likelihood, as well as more realistic
characterizations of the relationship between species abundance and average
body size of conspecific individuals. This suggests that the details of the
biological processes contain additional information for understanding community
structure that are not fully captured by the METE constraints in these systems.
Our approach provides a first step towards differentiating between process- and
constraint-based models of ecological systems and a general methodology for
comparing ecological models that make predictions for multiple patterns.Comment: 45 pages, 3 main figures, 3 tables, 2 appendices. arXiv admin note:
text overlap with arXiv:1308.073
Invasion of dwarf bamboo into alpine snow-meadows in northern Japan: pattern of expansion and impact on species diversity
Recently, a dwarf bamboo species,Sasa kurilensis; Poaceae, has invaded into alpine snow-meadows in the wilderness area of the Taisetsu Mountains, northern Japan. This dwarf bamboo species has a wide distribution range from lowland to alpine sites of snowy regions. Because of the formation of dense evergreen culms and an extensive rhizome system, other plants are excluded following invasion by this dwarf bamboo, resulting in low species diversity. Dwarf bamboo originally inhabited the leeward slopes of alpine dwarf pine (Pinus pumila) clumps in alpine regions. During the last 32 years, however, dwarf bamboo has expanded its distribution area by up to 47% toward snow-meadows, especially on southeastern facing slopes. This rapid change may be related to the decrease in soil moisture and expansion of the annual growing period caused by the recent acceleration of snowmelt time. A multiyear census revealed that the density of bamboo culms increased 30–150% during 2 years, and the annual expansion of bamboo rhizomes was 39 cm on average. In addition to the expansion of bamboo clumps by vegetative growth, the possibility of migration by seed dispersal was also suggested by a genet analysis. With the increase in culm density, the species richness of snow-meadow vegetation decreased to less than one-quarter of the original level due to intense shading by dwarf bamboo. The rapid vegetation change in these almost pristine alpine environments isolated from the human activity implies that global climate change already influences the alpine ecosystem
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