Luis A. Vélez-Espino

The COMPADRE Plant Matrix Database: an open online repository for plant demography.

Summary 1. Schedules of survival, growth and reproduction are key life-history traits. Data on how these traits vary among species and populations are fundamental to our understanding of the ecological conditions that have shaped plant evolution. Because these demographic schedules determine population

Recovery Potential Assessment for Lake Sturgeon in Canadian Designatable Units

Abstract Significant declines in the abundance of lake sturgeon Acipenser fulvescens across most of its North American range have led to abundances less than 10% of estimated minimum sustainable population sizes and, in some locations, less than 1% of historic abundances. These precipitous declines in abundance have resulted in most lake sturgeon populations being considered a conservation concern and have prompted management actions toward recovery. Here we present modeling in support of a recovery potential assessment, using stage-structured matrix models and population viability analysis to quantitatively assess allowable harm, recovery efforts, probabilities of recovery, and recovery time frames. From this assessment, we conclude that lake sturgeon populations are most sensitive to harm on adult survival and that some designatable units are highly sensitive to any level of harm. However, the scope for recovering lake sturgeon by improving adult survival is limited; instead, larger proportional increas...

Invasion dynamics of round goby (Neogobius melanostomus) in Hamilton Harbour, Lake Ontario

Most introduced non-native species fail to establish as a result of mortality or reproductive failure. An established population can increase the probability of survival and reproductive success of newly introduced individuals by reducing both Allee effects and demographic stochasticity. Previously, attention has been paid to the establishment phase of the invasion process and its probability modelled as a stochastic process, while the spread phase has received less attention. By analyzing data collected during the spread phase of an invasion of the round goby, Neogobius melanostomus, in Hamilton Harbour, Lake Ontario, we develop an analytical approach to backcalculate the time to establishment and to determine the time to habitat saturation. Our modelling shows that: (1) during the transition between arrival and establishment, propagule pressure in the form of new adults entering the area can be very low and still represent a significant probability of establishment; (2) much higher concentrations of juveniles would be needed to pose a significant risk of invasion; (3) the demographic contribution of propagule pressure during the spread phase is low and its total elimination will not halt population growth and spread; (4) a short elapsed time between arrival and establishment indicated that the transition between these two phases can be characterized as a deterministic process with high propagule pressure and low adult mortality rates; and, (5) very aggressive management actions would be needed to halt population growth after population establishment, suggesting that preventative measures are the most effective management options available to reduce risk of future invasions.

A synthesis of the ecological processes influencing variation in life history and movement patterns of American eel: towards a global assessment

American eel, Anguilla rostrata, is a catadromous fish that spawns in the Sargasso Sea and migrates to coastal waters and freshwater systems ranging from Greenland down the Atlantic coast to South America and has been regarded as comprising a panmictic population. American eel is in decline across much of its range. Research and management is primarily conducted at local to regional scales, yielding inconsistent research results and management recommendations that may be inhibited by large-scale processes. We review the research on American eel ecology demonstrating that its variable life history and movement patterns can be explained based on: (1) latitudinal productivity gradients; (2) ideal free habitat selection; (3) conditional evolutionarily stable life history strategies; (4) size at arrival to the coast (correlated with distance from the spawning grounds); and, (5) temperature variance and annual degree-day effects on somatic growth. Using these ecological processes, we outline how local and large-scale effects on American eel dynamics can be integrated in a panmictic (or quasi-panmictic) modelling framework to enable defensible predictions of population responses to anthropogenic and oceanic phenomena. Due to its widespread distribution and existing knowledge gaps, the conservation and management of American eel will require international cooperation.

Estimating establishment probabilities of Cladocera introduced at low density: an evaluation of the proposed ballast water discharge standards.

The International Maritime Organization has proposed ballast water discharge standards to reduce densities of taxa transported in ballast water. While reduced propagule pressure will almost certainly lower the risk of species introductions, we ask if the proposed standards will be effective against taxa capable of rapid population growth from small inocula, such as parthenogenetic taxa. We modified a diffusion approximation to calculate establishment probabilities as the probability of reaching a critical threshold density necessary to initiate sexual reproduction (and production of diapausing eggs for long-term persistence) before the onset of adverse environmental conditions. We parameterize our model for six Cladocera using growth rates measured during enclosure experiments conducted under favourable environmental conditions (i.e., using a precautionary approach). We then examine predicted establishment probabilities at different inoculum densities to determine the efficacy of the proposed ballast wate...

Ecological advantages of partial migration as a conditional strategy.

Partial migration is a widespread phenomenon characterized by migrant and resident forms from the same population. In phenotypically plastic taxa with indeterminate growth, resident and migrant ecophenotypes can differ in size and life history traits in ways expected to maximize fitness in the different habitats they exploit. Studies of partial migration in different taxa have advocated either density-dependence or environmental stochasticity as explanations for partial migration. We used a demographic approach for a virtual Brook Trout population to demonstrate the ecological consequences of partial migration under interacting density dependence and environmental stochasticity. The maintenance of partial migration as a conditional strategy in species/populations where resident and migrant forms exhibit life history asymmetries provides ecological advantages. We show that density-dependent migration is expected to increase population fitness under constant environmental conditions or low environmental variation, but decreases population fitness under high environmental variation. These conditions favor intermediate levels of migration as an advantageous tactic. However, there are threshold rates of return migration below which partial migration is no longer a viable tactic. Our modeling approach also allowed the exploration of the distribution of the population by life stage and habitat in response to the strength of density dependence, costs of migration, and return rates, and demonstrated the importance of the conservation of ecophenotypes in partially migratory populations.