El pasado 24 de abril falleció un amigo, el Profesor Welington Delitti, después de luchar duramente, y durante más de dos años, contra un cáncer. Welington era profesor de ecología en el Instituto de Biociencias de la Universidad de Sao Paulo (Brasil), donde dirigió a numerosos estudiantes; también tuvo un papel importante en la dirección del Instituto (director 2007-2011 y subdirector 2011-2015). Su investigación se centraba principalmente en el cerrado (sabanas) de Brasil, con especial énfasis en los ciclos de materia orgánica y nutrientes y, más recientemente, en la restauración y conservación de ese maravilloso ecosistema. Durante su visita a Valencia (España) trabajó sobre el efecto de la recurrencia del fuego en matorrales de coscoja (Quercus coccifera). Hizo una aportación importante a la ecología del cerrado, y muchos de sus trabajos fueron publicados en revistas científicas brasileñas e internacionales (ver lista de publicaciones aquí). Y fue él quien me mostró ese ecosistema tan interesante por primera vez.
Personalmente era una persona entrañable, buena, y muy comprometida con la universidad y la sociedad. Era muy apreciado en su universidad por su buena gestión del Instituto de Biociencias. Su carácter afable y tranquilo le llevaba a resolver los conflictos de la forma más socialmente correcta posible. Nos enseñó una manera de funcionar, y por ello, su legado es grande.
Welington Delitti en un Cerrado de Sao Paulo, Brasil 2008 (foto: JG Pausas)
Fotos de Welington Delitti tomadas entre 2008 y 2021. La foto de arriba-derecha, por Marcos Santos (USP Imagens, 2013); las 3 fotos de la fila de abajo y la del medio-izquierda, extraídas del Facebook de Welington (2018-2012); las otras 3 fotos son propias (2008, 2014; JG Pausas).
Ecology and evolutionary biology have focused on how organisms fit the environment. Less attention has been given to the idea that organisms can also modify their environment, and that these modifications can feed back to the organism, thus, providing a key factor for their persistence and evolution [1]. We propose that there are at least three independent lines of evidence emphasising these biological feedback processes at different scales (figure below): niche construction (population scale); alternative biome states (community scale); and the Gaia hypothesis (planetary scale). Flammability is an example of niche construction [2], and the forest-savanna mosaics are an example of the alternative biome states [3] (figure below).
The importance of feedback processes make us rethink traditional concepts like niche and adaptation. For instance, the idea of evolution as a process of adaptation to fit a pre-existing environment needs to be replaced by a ‘co-evolutionary’ species-environment approach. An implication is that the concept of species niche, and niche occupancy, is less relevant than traditionally thought. That is, organisms do not adapt to a pre-existing environment (available niche), they construct their environment and then both ‘co-evolve’. A higher level of fitness is the result of this coevolution. Feedbacks also provide an alternative framework for understanding spatial and temporal patterns of vegetation that differ from those based on gradual changes (e.g., gradient analysis and succession), and suggest that multi-stability and abrupt transitions in a given environment are common [3]; this also has implications for species’ niche modelling [4].
Earth is in transition to a new and warmer state due to anthropogenic forcing, and feedback thinking may help us understand the process. We suggest that incorporating feedback thinking and understanding how feedbacks may operate at different scales may help in opening our minds to key processes contributing to the dynamics and resilience of our biosphere.
Fig. 1. Examples of eco-evolutionary feedbacks at different organising levels: Niche construction (population; e.g. flammability), alternative biome states (community; forests and savannas) and Gaia (biosphere). The signs of the feedbacks indicate the most common type of feedback for each example. Evolutionary feedbacks represent the evolutionary processes at the different scales (from selection at the micro-evolutionary scale to the acquisition of key macro-evolutionary innovations). From [1].
References
[1] Pausas J.G. & Bond W.J. 2022. Feedbacks in ecology and evolution. Trends Ecol. Evol. [doi | pdf]
[2] Pausas J.G., Keeley J.E., Schwilk D.W. 2017. Flammability as an ecological and evolutionary driver. J. Ecol. 105: 289-297. [doi | wiley | pdf]
[3] Pausas J.G. & Bond W.J. 2020. Alternative biome states in terrestrial ecosystems. Trends Plant Sci. 25: 250-263. [doi | sciencedirect | cell | pdf]
[4] Pausas J.G. & Bond W.J. 2021. Alternative biome states challenge the modelling of species’ niche shifts under climate change. J. Ecol. 109: 3962-3971. [doi | wiley | pdf]
Many plants concentrate their seedling recruitment after the passage of a fire. This is because postfire conditions are especially optimal for germination and establishment of many species as fires create extensive vegetation gaps that have high resource availability, minimal competition, and low pathogen load. Thus we propose that fireprone ecosystems create ideal conditions for the selection of seed dormancy as fire provides a mechanism for dormancy release and optimal conditions for germination [1]. We compiled data from a wide range of fire-related germination experiments for species in different ecosystems across the globe and identified four dormancy syndromes: heat-released (physical) dormancy, smoke-released (physiological) dormancy, non-fire-released dormancy, and non-dormancy. In fireprone ecosystems, fire, in the form of heat and/or chemical by-products (collectively termed ‘smoke’), are the predominant stimuli for dormancy release and subsequent germination, with climate (cold or warm stratification) and light sometimes playing important secondary roles. Fire (heat or smoke)-released dormancy is best expressed where woody vegetation is dense and fires are intense, i.e. in crown-fire ecosystems (e.g., mediterranean-type ecosystems). In grassy fireprone ecosystems (e.g. savannas), where fires are less intense but more frequent, seed dormancy is less common and dormancy release is often not directly related to fire (non-fire-released dormancy). Fire-released dormancy is rare to absent in arid ecosystems and rainforests. Heat-released dormancy can be traced back to fireprone floras in the ‘fiery’ mid-Cretaceous, followed by smoke-released dormancy, with loss of fire-related dormancy among recent events associated with the advent of open savannas and non-fireprone habitats. Anthropogenic influences are now modifying dormancy-release mechanisms, usually decreasing the role of fire. We conclude that contrasting fire regimes are a key driver of the evolution and maintenance of diverse seed dormancy types in many of the world’s natural ecosystems.
Fig. 1. Percentage germination of 68 populations or species subjected to simulated fire- (y axis) and summer-type (warm stratification) temperature (x-axis) (C., Cistus; F., Fumana; U., Ulex; A., Acacia; M., Mimosa). Points above the dotted line (1:1) have higher germination levels after fire heat than after summer heat. Note that all points at or below the line are for species in savannas [S], while the others are from mediterranean shrublands and other crown-fire ecosystems. That is, in crown-fire ecosystems, fire is the most likely selective agent for dormancy. From [1].
Fig. 2. Dated phylogeny for major clades in the New and Old World Cistaceae together with closely related ancestral clades. Pie charts at the tips show the fraction of species that occur in crown-fire ecosystems (red), surface-fire ecosystems (orange), those with physical dormancy – hard seeds (green), and those with heat-released dormancy (blue). Blank sectors mean that the trait is absent. Letters at the tips refer to growth forms in the clade (T, tree; S, shrub or subshrub; H, herb/annual). Black dots indicate the crown age of diversification of the corresponding clade. From [1].
References
[1] Pausas J.G. & Lamont B.B. 2022. Fire-released seed dormancy – a global synthesis. Biological Reviews [doi | pdf | supp. mat. | data (figshare)]
