Occurrence and abundance models of threatened plant species: Applications to mitigate the impact of hydroelectric power dams

Abstract

In situ and ex situ plant conservation Environmental assessment Model validation a b s t r a c t Species occurrence and abundance models are important tools that can be used in biodiversity conservation, and can be applied to predict or plan actions needed to mitigate the environmental impacts of hydropower dams. In this study our objectives were: (i) to model the occurrence and abundance of threatened plant species, (ii) to verify the relationship between predicted occurrence and true abundance, and (iii) to assess whether models based on abundance are more effective in predicting species occurrence than those based on presence-absence data. Individual representatives of nine species were counted within 388 randomly georeferenced plots (10 m × 50 m) around the Barra Grande hydropower dam reservoir in southern Brazil. We modelled their relationship with 15 environmental variables using both occurrence (Generalised Linear Models) and abundance data (Hurdle and Zero-Inflated models). Overall, occurrence models were more accurate than abundance models. For all species, observed abundance was significantly, although not strongly, correlated with the probability of occurrence. This correlation lost significance when zero-abundance (absence) sites were excluded from analysis, but only when this entailed a substantial drop in sample size. The same occurred when analysing relationships between abundance and probability of occurrence from previously published studies on a range of different species, suggesting that future studies could potentially use probability of occurrence as an approximate indicator of abundance when the latter is not possible to obtain. This possibility might, however, depend on life history traits of the species in question, with some traits favouring a relationship between occurrence and abundance. Reconstructing species abundance patterns from occurrence could be an important tool for conservation planning and the management of threatened species, allowing scientists to indicate the best areas for collection and reintroduction of plant germplasm or choose conservation areas most likely to maintain viable populations.

Environmental favourability as a cost‐efficient tool to estimate carrying capacity

“…Although SDMs have been successfully used in a large variety of studies, the relationship between the output of presence–absence‐based models and abundance has rarely been assessed, and when this has been done, inconsistent results have been obtained (see Pearce & Ferrier, ; Nielsen et al ., ; Jiménez‐Valverde et al ., ; Real et al ., ; VanDerWal et al ., ; Guarino et al ., ; Torres et al ., ; Wilson, ; Gutiérrez et al ., ). Given that SDMs reflect, in some way, environmental suitability and that more individuals are assumed to inhabit the most suitable areas (Sarà, ; VanDerWal et al ., ; but see Van Horne, ), it would be of interest to determine the extent to which the occurrence‐based suitability/abundance relationship holds, so that conclusions based on presence–absence models could be appropriately used to identify areas of conservation concern.…”

“…The relationship between the P values derived from the 10‐fold partition (see below) and the number of breeding pairs per UTM 10 × 10 km square was analysed. Firstly, Spearman correlation was calculated between the two variables; this was conducted by using the entire dataset and also by excluding locations with F ≤ 0.2 (see Muñoz et al ., ) to test whether a positive significant correlation was simply the product of the discrimination capacity of the model (Jiménez‐Valverde et al ., ; VanDerWal et al ., ; Guarino et al ., ). Secondly, the relationship between P and density is expected to be triangular; that is, low P values would correspond to low numbers of breeding pairs, whereas high P values would correspond to either low or high numbers of breeding pairs (see VanDerWal et al ., ).…”

Comparing estimates of population change from occupancy and mark–recapture models for a territorial species

“…), but also at smaller scales (Estrada and Arroyo , Guarino et al. ). The governing theory is that there will be a positive inter‐ and intraspecific relationship between regional occupancy and local abundance (Zuckerberg et al.…”

Modelling Tools to Analyze and Assess the Ecological Impact of Hydropower Dams

“…Ecological models can support decision making in environmental and conservation management [16] and have already been applied to assess the impact of dams on fish [17][18][19][20][21][22], macroinvertebrates [23][24][25], amphibians [26] and vegetation [27][28][29]. Models are being increasingly used in environmental assessment, planning and management [30].…”