Modelado de hábitats fragmentados mediante redes complejas en el marco de la ecología de la conservación / Modeling of fragmented habitats through complex networks in the framework of conservation ecology

Llauradó Harvey, Pedro (2022) Modelado de hábitats fragmentados mediante redes complejas en el marco de la ecología de la conservación / Modeling of fragmented habitats through complex networks in the framework of conservation ecology. Master in Physical Sciences, Universidad Nacional de Cuyo, Instituto Balseiro.

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Abstract in Spanish

Se implementó un modelo metapoblacional espacialmente explícito para la simulación de un sistema depredador-presa inmerso en un hábitat fragmentado, compuesto por un conjunto de parches habitables conectados mediante enlaces de dispersión lenta. Un formalismo particularmente adecuado para describir este tipo de hábitats es el de la teoría de grafos. Específicamente, en este trabajo se implementaron Redes de Umbral Geográfico, cuyos nodos poseen coordenadas espaciales y donde las conexiones se establecen por proximidad. Para agregar un mayor nivel de detalle al modelo, se utilizaron multigrafos, por lo que cada especie posee su propio conjunto de aristas, de manera que la probabilidad de acceder a un parche dado es distinta para presas y depredadores. Se encontró una amplia región del espacio de fases en la cual la coexistencia entre ambas especies es posible. La exploración de la especificidad en la dieta del depredador y de la presión de depredación reveló una alta sensibilidad del sistema a los valores de los parámetros utilizados. Esto es relevante desde un punto de vista ecológico, ya que remarca el hecho de que ciertos ecosistemas pueden sufrir modificaciones sustanciales frente a pequeños cambios en la forma en la que las especies interactúan. Otro resultado destacable es que las presas presentan un efecto de refugio: el tiempo de vida medio es mayor en los parches donde el depredador tiene baja conectividad. Por ultimo, se estudió el impacto de diferentes estrategias para la destrucción y reconstrucción de parches. Se encontró que el sistema presenta histéresis, es decir, la densidad de ambas especies puede diferir para un mismo número de parches removidos según se esté ejecutando un proceso de destrucción o de restauración de la red. Esta diferencia está asociada a la fragmentación de la componente gigante en subgrafos pequeños, donde la supervivencia se ve dificultada ya que las fluctuaciones estocásticas se hacen comparables al tamaño del subsistema. La destrucción de nodos donde la presa posee grado elevado resultó la más perjudicial para el ecosistema en su conjunto, ya que la componente gigante de la presa se fragmenta mucho antes que la del depredador. De forma analogía, aquellas estrategias que priorizan la restauración de parches donde la presa tiene mayor grado son las más eficientes para la recuperación simultánea de ambas especies, ya que la presa percibe una rápida mejora en la conectividad. Este aumento en su colonización efectiva se traduce en un incremento en su densidad, beneficiando indirectamente a los depredadores. Por el contrario, si los parches que se restauran maximizan el flujo de depredadores en la red, el impacto sobre las presas es muy negativo, por lo que no es una estrategia recomendable si lo que se busca es una recuperación homogénea del ecosistema. Los hábitats fragmentados resultan ubicuos en la naturaleza. La destrucción de estos ecosistemas es considerada la mayor causa de la pérdida de biodiversidad actual. Estudiar el impacto que las diferentes estrategias de restauración pueden tener en la recuperación de estos hábitats es de vital importancia para la toma de decisiones en la gestión de los recursos naturales y para el desarrollo de políticas optimas de conservación.

Abstract in English

A spatially explicit metapopulation model was implemented to simulate a predatorprey system immersed in a fragmented habitat, composed of a set of habitable patches connected by slow dispersal links. A particularly suitable formalism to describe this type of habitat is that of graph theory. Specifically, in this work Geographic Threshold Networks were implemented, whose nodes have spatial coordinates and where connections are established by proximity. To add a higher level of detail to the model, multigraphs were used, where each species has its own set of edges, so the probability of accessing a given patch depends upon the species considered. A wide region of the phase space was found in which the coexistence between both species is possible. The exploration of the specificity in the predator’s diet and of the predation pressure revealed a high sensitivity of the system to the values of the parameters used. This is relevant from an ecological point of view, since it highlights the fact that certain ecosystems can undergo substantial modifications in the face of small changes in the way in which species interact. Another noteworthy result is that the prey presents a refuge effect: the mean lifetime is longer in patches where the predator has low connectivity. Finally, the impact of different strategies for the destruction and reconstruction of patches was studied. It was found that the system presents hysteresis, that is, the density of both species can differ for the same number of patches removed depending on whether a network destruction or restoration process is being executed. This difference is associated with the fragmentation of the giant component into small subgraphs, where survival is harder since stochastic fluctuations become comparable to the size of the subsystem. The destruction of nodes where the prey has a high degree was the most detrimental to the ecosystem as a whole, since the giant component of the prey fragments much earlier than that of the predator. Similarly, those strategies that prioritize the restoration of patches where the prey has a higher grade are the most efficient for the simultaneous recovery of both species, since the prey perceives a rapid improvement in connectivity. This increase in their effective colonization translates into an increase in their density, indirectly benefiting predators. On the contrary, if the patches that are restored maximize the flow of predators in the network, the impact on the prey is very negative, so it is not a recommended strategy if a homogeneous recovery of the ecosystem is sought. Fragmented habitats are ubiquitous in nature. The destruction of these ecosystems is considered the main cause of current biodiversity loss. Studying the impact that different restoration strategies can have on the recovery of these habitats is of vital importance for decision-making in the management of natural resources and for the development of optimal conservation policies.

Item Type:Thesis (Master in Physical Sciences)
Keywords:[Mathematical ecology; Ecología matemática; Metapopulations; Metapoblaciones; Predator-prey model; Modelo depredador-presa; Fragmented habitat; Habitat fragmentado; Complex Networks; Redes complejas; Patch destructions; Destrucción de parches]
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Subjects:Physics > Dinámica poblacional de especies ecológicas
Divisions:Gcia. de área de Investigación y aplicaciones no nucleares > Gcia. de Física > Sistemas complejos y altas energías > Física estadística interdisciplinaria
ID Code:1154
Deposited By:Tamara Cárcamo
Deposited On:03 Aug 2023 16:06
Last Modified:03 Aug 2023 16:06

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