Sources of Mortality in Bald Eagles in Michigan, 1986–2017

As bald eagle populations recover, defining major sources of mortality provides managers important information to develop management plans and mitigation efforts. We obtained data from necropsies on 1,490 dead bald eagles (Haliaeetus leucocephalus) collected in Michigan, USA, conducted from 1986 to 2017 to determine causes of death (COD). Trauma and poisoning were the most common primary COD categories, followed by disease. Within trauma and poisoning, vehicular trauma (n = 532) and lead poisoning (n = 176) were the leading COD subcategories, respectively. Females comprised a greater number of carcasses for most COD diagnoses. The proportion of trauma and poisoning CODs significantly increased in the last few years of the study in comparison to a select few years at the beginning. Trauma CODs were greater in autumn months during whitetail deer (Odocoileus virginianus) breeding and hunting seasons and in February, when aquatic foraging is unavailable and eagles are likely forced to scavenge along roadsides. Poisoning CODs were greatest in late winter and early spring months, when deer carcasses containing lead ammunition, which are preserved by the cold weather, also become a supplemental food source. The major infectious disease CODs, West Nile virus and botulism (Clostridium botulinum type E), were more prevalent during summer months. We recommend moving road-killed carcasses, especially white-tailed deer, from the main thoroughfare to the back of the right-of-way, and the transition from lead ammunition and fishing tackle to non-toxic alternatives to decrease these main anthropogenic sources of mortality for bald eagles, and other scavenger species. © 2020 The Wildlife Society.     

Integral projection models perform better for small demographic data sets than matrix population models: a case study of two perennial herbs

1. Matrix population models are widely used to describe population dynamics, conduct population viability analyses and derive management recommendations for plant populations. For endangered or invasive species, management decisions are often based on small demographic data sets. Hence, there is a need for population models which accurately assess population performance from such small data sets.
2. We used demographic data on two perennial herbs with different life histories to compare the accuracy and precision of the traditional matrix population model and the recently developed integral projection model (IPM) in relation to the amount of data.
3. For large data sets both matrix models and IPMs produced identical estimates of population growth rate (λ). However, for small data sets containing fewer than 300 individuals, IPMs often produced smaller bias and variance for λ than matrix models despite different matrix structures and sampling techniques used to construct the matrix population models.
4. Synthesis and applications . Our results suggest that the smaller bias and variance of λ estimates make IPMs preferable to matrix population models for small demographic data sets with a few hundred individuals. These results are likely to be applicable to a wide range of herbaceous, perennial plant species where demographic fate can be modelled as a function of a continuous state variable such as size. We recommend the use of IPMs to assess population performance and management strategies particularly for endangered or invasive perennial herbs where little demographic data are available.     

生境片断化对濒危植物景东翅子树种群结构与动态的影响

生境的破坏及其片断化是生物多样性丧失的主要原因, 了解生境片断化对植物种群动态的影响十分必要。本文比较分析了不同大小生境片断(5 ha和15 ha)和连续森林中濒危植物景东翅子树(Pterospermum kingtungense)种群的结构与动态, 目的是明确影响景东翅子树种群动态的关键生活史阶段及其种群保护的目标, 为濒危植物种群保护和管理策略的制定提供科学依据。在上述3种生境中分别设立3个50 m × 100 m的1.5 ha固定样地, 调查景东翅子树所有个体的胸径(其中幼苗和幼树为地径)和高度、个体的存活及幼苗的补充情况。基于上述统计参数, 建立预测种群动态的Lefkovitch矩阵模型, 同时应用矩阵模型的弹性分析方法量化种群统计参数对种群增长率的相对贡献。结果表明: (1)在5 ha和15 ha生境片断及连续森林各1.5 ha的样地中, 2018年首次调查到景东翅子树的个体数分别为34、82和88株, 2019年复查时的个体数分别为33、82和87株。3种生境中景东翅子树种群的年龄结构均以幼树为主, 但5 ha生境片断森林缺乏幼苗和大树(包括成树和亚成树), 而15 ha生境片断森林幼苗较丰富。(2)在3种生境中景东翅子树种群的增长率等于1 (15 ha生境片断)或趋近于1 (5 ha生境片断和连续森林), 说明不同生境中的景东翅子树种群比较稳定, 这主要是因为其各生活史阶段的存活率均较高。(3)景东翅子树成树和亚成树阶段的存活率对种群增长率的贡献最大, 是影响其种群动态的关键生活史阶段。因此对于大树(包括成树和亚成树)的保护是极度濒危植物景东翅子树种群维持的关键。研究结果揭示小生境片断降低了景东翅子树种群的数量, 改变了种群的结构, 但对种群动态的影响效应尚未显现。因此对于这些小生境片断中濒危植物种群的保护和恢复是可行的, 也是有价值的。     

An approach to the nonlinear dynamics of Russian wheat aphid population growth with the cusp catastrophe model

Many insect field populations, especially aphids, often exhibit irregular and even catastrophic fluctuations. The objective of the present study is to explore whether or not the population intrinsic rates of growth ( r _m) obtained under laboratory conditions can shed some light on the irregular changes of insect field populations. We propose to use the catastrophe theory, one of the earliest nonlinear dynamics theories, to answer the question. To collect the necessary data, we conducted a laboratory experiment to investigate population growth of the Russian wheat aphid (RWA), Diuraphis noxia (Mordvilko), in growth chambers. The experiment was designed as the factorial combinations of five temperatures and five host plant-growth stages (25 treatments in total): 1800 newly born RWA nymphs arranged in the 25 treatments (each treatment with 72 repetitions) were observed for their development, reproduction and survival through their entire lifetimes. After obtaining the population intrinsic rates of growth ( r _m) from the experimental data under various environmental conditions, we built a cusp catastrophe model for RWA population growth by utilizing r _m as the system state variable, and temperature and host plant-growth stage as control variables. The cusp catastrophe model suggests that RWA population growth is intrinsically catastrophic , and dramatic jumps from one state to another might occur even if the temperature and plant-growth stage change smoothly . Other basic behaviors of the cusp catastrophe model, such as catastrophic jumps , hystersis and divergence , are also expected in RWA populations. These results suggest that the answer to the previously proposed question should be yes.     

Population modelling of Gelidium sesquipedale (Rhodophyta, Gelidiales)

A matrix population model of Gelidium sesquipedale, a commercial agarophyte from the Northeast Atlantic, was developed based on demographic data obtained during two years in a commercial stand of Cape Espichel, Portugal. G. sesquipedale individuals were classified into categories such as life cycle phase, spores, juveniles and adult frond size, because the species vital rates, fecundity, fertility, survival, growth and breakage depend on them. We also exemplify the use of a user-friendly modelling software, Stella, to develop a structured-population model. This is the first time this software has been used to model the demography of seaweed populations. The Stella model developed here behaved very similarly to the matrix model, because of its particular construction, which causes the forcing functions to be discrete rather than continuous. The relative importance of spore recruitment and vegetative growth of new fronds in both population growth and population structure was investigated. Elasticity analysis suggests that vegetative recruitment is the most important demographic parameter controlling population growth together with survival and transitions between juveniles (1–6 cm fronds) and class 1 fronds (6–9 cm fronds). On the other hand, sexual reproduction may, by itself, efficiently control the relative proportion of gametophytes and tetrasporophytes in the population, even though its contribution to recruitment is extremely small. A 40% difference in the growth rates of gametophyte and tetrasporophyte submatrices resulted from natural differences in spore recruitment rates. This revised version was published online in June 2006 with corrections to the Cover Date.