37 research outputs found
High temporal variability in the occurrence of consumer-resource interactions in ecological networks
Ecological networks are theoretical abstractions that represent ecological
communities. These networks are usually defined as static entities, in which
the occurrence of a particular interaction between species is considered fixed
despite the intrinsic dynamics of ecological systems. However, empirical
analysis of the temporal variation of trophic interactions is constrained by
the lack of data with high spatial, temporal, and taxonomic resolution. Here,
we evaluate the spatiotemporal variability of multiple consumer-resource
interactions of large marine networks. The tropic interactions of all of the
analyzed networks had low temporal persistence, which was well described by a
common exponential decay in the rank-frequency relationship of
consumer-resource interactions. This common pattern of low temporal persistence
was evident despite the dissimilarities of environmental conditions among
sites. Between-site rank correlations of frequency of occurrence of
interactions ranged from 0.59 to 0.73. After removing the interactions with
<50% frequency, the between-site correlations decreased to values between 0.60
and 0.28, indicating that low-frequency interactions accounted for the apparent
similarities between sites. Our results showed that the communities studied
were characterized by few persistent interactions and a large number of
transient trophic interactions. We suggest that consumer-resource temporal
asynchrony in addition to varying local environmental conditions and
opportunistic foraging could be among the mechanisms generating the observed
rank-frequency relationship of trophic interactions. Therefore, our results
question the analysis of ecological communities as static and persistent
natural entities and stress the need for strengthening the analysis of temporal
variability in ecological networks and long-term studies.Comment: 21 pages, 3 figure
Educaci\uf3n Cient\uedfica y Evolutiva en Chile: Problemas Funcionales y Confictos entre Ense\uf1ar y Aprender
116 a\uf1os de la Revista Chilena de Historia Natural: Breve relato de dos antes y un despu\ue9s
Biogeograf铆a marina de Chile continental Marine biogeography of continental Chile
Por casi un siglo, varios autores han analizado los patrones de distribuci贸n de la fauna y flora marina del Pac铆fico de Sudam茅rica y de la costa de Chile en particular, con el prop贸sito de establecer el n煤mero de las unidades biogeogr谩ficas presentes. Si bien los patrones generales actuales son relativamente bien conocidos, la mayor铆a de los estudios se ha enfocado en las discontinuidades distribucionales y en propuestas de clasificaci贸n m谩s que en los factores y procesos din谩micos que han formado las unidades espaciales identificadas. Aun en el caso de las clasificaciones, las conclusiones publicadas se basan principalmente en el an谩lisis de uno o pocos grupos seleccionados, y presentan diferencias importantes en los criterios de selecci贸n de los grupos, el n煤mero de especies involucrado y la metodolog铆a usada. Por otra parte, las discrepancias entre estudios espec铆ficos tienden a obscurecer un fen贸meno relevante y de mayor escala como es la din谩mica de las biotas, uno de los aspectos biogeogr谩ficos menos conocidos en Chile. En tal contexto, este trabajo presenta una revisi贸n de literatura sobre la biogeograf铆a marina de Chile y sus aspectos asociados, con los siguientes objetivos: (a) resumir las caracter铆sticas oceanogr谩ficas, clim谩ticas y geomorfol贸gicas de la costa continental de Chile; (b) discutir 27 clasificaciones biogeogr谩ficas publicadas para la costa chilena, analizando los criterios y procedimientos usados por los autores, sus conclusiones principales, y la concordancia entre los estudios; (c) evaluar los procesos dispersivos y vicariantes asociados a los desplazamientos y modificaciones de las biotas de la regi贸n, en funci贸n de los antecedentes disponibles sobre las condiciones existentes y los principales eventos ocurridos durante los per铆odos Terciario y Cuaternario; y (d) proponer un escenario de cambio biogeogr谩fico basado en determinantes hist贸ricas y su influencia en la formaci贸n, car谩cter y din谩mica de distribuci贸n de biotas en la costa chilena, con 茅nfasis en la identificaci贸n y naturaleza biogeogr谩fica de las principales unidades espaciales. A partir de la informaci贸n anterior, se propone una hip贸tesis de clasificaci贸n biogeogr谩fica al nivel de biotas, no necesariamente concordante con estudios previos al nivel de fauna o flora. Esta clasificaci贸n identifica tres unidades espaciales mayores: un 谩rea sur que incluye a una biota austral (Provincia Magall谩nica), un 谩rea norte que incluye una biota templada-c谩lida (Provincia Peruana), y un 谩rea Intermedia extensa (no transicional) que incluye componentes mixtos de biota sin car谩cter ni rango biogeogr谩fico definido. Se discute adem谩s la diferente naturaleza de dos zonas transicionales situadas en los l铆mites del 谩rea Intermedia, una transici贸n de contacto hacia el norte y una transici贸n inducida hacia el sur, que se habr铆an generado por migraciones de biota y eventos glacio-tect贸nicos respectivamente<br>For almost a century, a number of authors have analyzed the distribution patterns of the marine fauna and flora in the South American Pacific and particularly along the coast of Chile, with the purpose of determining the number of existing biogeographical units. Although the general, present day patterns are relatively well known, most studies have focused on distributional breaks and classification proposals rather than on the factors and dynamic processes that formed the identified spatial units. Even in the case of biogeographical classifications, published conclusions are based mainly on the analysis of one or few selected groups, exhibiting important differences in their criteria for selecting groups, the number of species involved, and their methodology. On the other hand, diverging conclusions among particular studies tend to obscure the more relevant, large-scale phenomenon of biota dynamics, one of the less known biogeographic aspects in Chile. Within that context, this paper presents a literature review on the marine biogeography of Chile and related subjects, with the following objectives: (a) to summarize the oceanographic, climatic and geomorphologic characteristics of the Chilean continental coast; (b) to discuss 27 biogeographic classifications published for the Chilean coast, analyzing both the procedures and criteria used by their authors, along with their main conclusions and agreements; (c) to assess the vicariant and dispersal processes associated with the displacement and modification of the regional biotas, regarding the available antecedentes on the prevailing conditions and main events during the Tertiary and Quaternary periods; and (d) to propose a scenario of biogeographic change based on historical determinants and their influence on the formation, character, and dynamics of biotas along the Chilean coast, emphasizing the identification and biogeographic nature of the main spatial units. From the preceding information, I propose a hypothesis of biogeographic classification for the level of biotas, not necessarily coincident with prior studies at lower levels such as flora or fauna. This classification identifies three major spatial units: a southern area which comprises an austral biota (Magellan Province), a northern area which comprises a warm-temperate biota (Peruvian Province), and a non transitional, Intermediate Area including mixed components of biota and exhibiting a poor biogeographic definition of both its character and hierarchical rank. I also discuss the different nature of two transitional zones located at the boundaries of the Intermediate Area, a southward induced transition and a northward contact transition, likely produced by the migration of biotas and glacial-tectonic events, respectivel
Diversidad, distribuci贸n y abundancia de especies en ensambles intermareales rocosos
Multiple sources of variation, including
biogeographic processes, upwelling and El Ni帽o, have
differential effects on rocky intertidal communities over the
north-central coast of Chile, and they could generate a high
variability in diversity, particularly at a regional scale. In this
context, species richness, dominance, evenness and composition
were assessed in 17 sessile assemblages located between 18潞
and 34潞S, along with the abundance and distribution of their
68 constituent species, for determining their patterns of
variation at different spatial scales. Different analyses showed,
among other results, that: (a) excepting species composition,
the spatial variation of all diversity attributes at the assemblage
level was explained almost entirely (83-100%) by local factors;
(b) the variation in species richness at the scale of the sampling
unit (0.25 m2) explained more than 61% of the variance,
reflecting an apparent pattern of saturation; (c) at a geographical
scale, rarity in both distribution and abundance was the
prevailing trait, and these two variables were positively
correlated at all spatial scales; (d) common (core) species
showed a low spatial variability in abundance and tended to be
the same in all assemblages; and (e) taxonomic composition
was the only attribute showing regional differences, related with
a higher beta diversity and a higher level of rarity in northern
Chile, which also appeared to be completely included within
the Peruvian biogeographic Province. The results suggest that
local and small-scale processes could be important determinants
of diversity in these assemblages.M煤ltiples fuentes de variaci贸n incluyendo
procesos biogeogr谩ficos, la surgencia y El Ni帽o, afectan
diferencialmente a las comunidades intermareales rocosas en
Chile centro-norte, y podr铆an generar una alta variabilidad en
sus patrones de diversidad, particularmente a escala regional.
En este contexto se evalu贸 la riqueza, dominancia, uniformidad
y composici贸n de 17 ensambles s茅siles ubicados entre los 18潞
y 34潞S, as铆 como la abundancia y distribuci贸n de sus 68 especies
constituyentes, para determinar sus patrones de variaci贸n en
distintas escalas espaciales. Una serie de an谩lisis mostr贸, entre
otros resultados, que: (a) exceptuando la composici贸n, la
variaci贸n espacial de todos los atributos de diversidad a escala
del ensamble fue explicada casi enteramente (83-100%) por
factores locales; (b) la variaci贸n en riqueza espec铆fica a escala
de la unidad muestral (0,25 m2) explic贸 m谩s del 61% de la
varianza, y reflej贸 un patr贸n aparente de saturaci贸n; (c) a escala
geogr谩fica, la rareza en distribuci贸n y abundancia fueron los
rasgos predominantes, y ambas variables se correlacionaron
positivamente en todas las escalas espaciales; (d) las especies
m谩s comunes mostraron una baja variabilidad espacial en
abundancia y tendieron a ser las mismas en todos los ensambles;
y (e) la composici贸n taxon贸mica fue el 煤nico atributo que revel贸
diferencias regionales, asociadas a una mayor diversidad beta
y mayor nivel de rareza en Chile norte, la cual adem谩s estar铆a
incluida completamente en la Provincia biogeogr谩fica Peruana.
Los resultados sugieren que los procesos locales y de peque帽a
escala podr铆an ser determinantes importantes de la diversidad
en los ensambles s茅siles
Educaci贸n Cient铆fica y Evolutiva en Chile: Problemas Funcionales y Confictos entre Ense帽ar y Aprender Science and Evolution Education in Chile: Functional Problems and Conficts between Teaching and Learning
En Chile, la educaci贸n media (secundaria) y universitaria de pregrado, y la conexi贸n entre ellas, son los puntos m谩s sensibles de la educaci贸n cient铆fca en biolog铆a y evoluci贸n, que estuvo seriamente deprimida hacia fnes del siglo XX. No obstante, hoy enfrentamos un escenario de transici贸n favorable donde convergen tres factores capaces de potenciar la alfabetizaci贸n biol贸gica en sentido amplio: un nuevo curr铆culum secundario que incluye un fuerte componente biol贸gico, con 茅nfasis en evoluci贸n y ecolog铆a; una reactivaci贸n de la formaci贸n pedag贸gica a nivel universitario; y un desarrollo cient铆fco creciente en el 谩rea de biolog铆a evolutiva. Sin embargo, estos factores a煤n est谩n conectados d茅bilmente, y su mejor articulaci贸n podr铆a contribuir a mejorar signifcativamente la retroalimentaci贸n entre los componentes del sistema educativo, y a resolver algunos confictos dial茅cticos entre ense帽ar y aprender que se generan en diferentes niveles jer谩rquicos del mismo sistema. El reforzamiento de la interdisciplinaridad entre biolog铆a y pedagog铆a en la formaci贸n de nuevos profesores ser铆a un factor clave, ya que el profesor secundario parece ser la piedra angular del sistema educativo, adem谩s de jugar un rol crucial en la formaci贸n inicial de los futuros cient铆fcos.<br>In Chile, high school (secondary) and university undergraduate levels, and their connection, are the most sensitive points of science education in biology and evolution, which was seriously depressed at the end of the 20th century. Nonetheless, we face today a favourable transitional scenario where three converging factors are able to foster science literacy in a wide sense: a new high school curriculum including a strong biological component, with emphasis on evolution and ecology; a reactivation of university formation of secondary pedagogues; and a growing scientifc development in the feld of evolutionary biology. However, these factors are still weakly connected, and strengthening their articulation might improve signifcantly the feedback between all components of the Chilean educational system, helping to solve some dialectic conficts between teaching and learning that originate at different hierarchical levels of the same system. The reinforcement of interdisciplinarity between biology and pedagogy in the process of formation of new teachers would be a key factor, because the high school teacher turns to be the cornerstone of the educational system, in addition playing a crucial role in the initial formation of the future scientists