Fred Jopp

Modeling seasonal dynamics of small fish cohorts in fluctuating freshwater marsh landscapes

Small-bodied fishes constitute an important assemblage in many wetlands. In wetlands that dry periodically except for small permanent waterbodies, these fishes are quick to respond to change and can undergo large fluctuations in numbers and biomasses. An important aspect of landscapes that are mixtures of marsh and permanent waterbodies is that high rates of biomass production occur in the marshes during flooding phases, while the permanent waterbodies serve as refuges for many biotic components during the dry phases. The temporal and spatial dynamics of the small fishes are ecologically important, as these fishes provide a crucial food base for higher trophic levels, such as wading birds. We develop a simple model that is analytically tractable, describing the main processes of the spatio-temporal dynamics of a population of small-bodied fish in a seasonal wetland environment, consisting of marsh and permanent waterbodies. The population expands into newly flooded areas during the wet season and contracts during declining water levels in the dry season. If the marsh dries completely during these times (a drydown), the fish need refuge in permanent waterbodies. At least three new and general conclusions arise from the model: (1) there is an optimal rate at which fish should expand into a newly flooding area to maximize population production; (2) there is also a fluctuation amplitude of water level that maximizes fish production, and (3) there is an upper limit on the number of fish that can reach a permanent waterbody during a drydown, no matter how large the marsh surface area is that drains into the waterbody. Because water levels can be manipulated in many wetlands, it is useful to have an understanding of the role of these fluctuations.

The ecological effect of phenotypic plasticity — Analyzing complex interaction networks (COIN) with agent-based models

Abstract Analyzing complex dynamics of ecological systems is complicated by two important facts: First, phenotypic plasticity allows individual organisms to adapt their reaction norms in terms of morphology, anatomy, physiology and behavior to changing local environmental conditions and trophic relationships. Secondly, individual reactions and ecological dynamics are often determined by indirect interactions through reaction chains and networks involving feedback processes. We present an agent-based modeling framework which allows to represent and analyze ecological systems that include phenotypic changes in individual performances and indirect interactions within heterogeneous and temporal changing environments. We denote this structure of interacting components as COmplex Interaction Network (COIN). Three examples illustrate the potential of the system to analyze complex ecological processes that incorporate changing phenotypes on the individual level: • A model on fish population dynamics of roach ( Rutilus rutilus ) leads to a differentiation in fish length resulting in a conspicuous distribution that influences reproduction capability and thus indirectly the fitness. • Modeling the reproduction phase of the passerine bird Erithacus rubecula (European Robin) illustrates variation in the behavior of higher organisms in dependence of environmental factors. Changes in reproduction success and in the proportion of different activities are the results. • The morphological reaction of plants to changes in fundamental environmental parameters is illustrated by the black alder ( Alnus glutinosa ) model. Specification of physiological processes and the interaction structure on the level of modules allow to represent the reaction to changes in irradiance and temperature accurately. Applying the COIN-approach, individual plasticity emerges as a structural and functional implication in a self-organized manner. The examples illustrate the potential to integrate existing approaches to represent detailed and complex traits for higher order organisms and to combine ecological and evolutionary aspects.

Perspectives in Ecological Modelling

In the chapters of this textbook we have presented a broad panorama of the network of discourse from which Ecological Modelling emerged and grew. Starting from the very early days, we have proceeded to give an overview of a wide spectrum of currently available approaches. Then, after looking at a selection of prominent model applications, we discussed how to assess model validity.

Establishment of laurel forest vegetation in adjacent secondary forest in central Japan

Distributions of lucidophyllous species are limited due to the fragmentation of laurel forest. On Komayama Hill in central Japan, we evaluated the colonization of typical lucidophyllous vascular plants from a 350-year-old laurel forest into adjacent abandoned secondary forest for conservation and restoration purposes. A total of 14 consecutive subplots were established along the vegetation border between the two forests (length, 30xa0m; width, 5xa0m), extending 70xa0m into the secondary forest; 18 quadrats of old-growth forest were surveyed. Edge effects of old-growth forest were found to play an important role in re-establishing lucidophyllous saplings and seedlings in the secondary forest. In particular, the abundances of the four dominant canopy species of the old-growth forest significantly decreased with increasing distance. Hence, they are expected to colonize further into the secondary forest and, ultimately, to dominate the canopy. However, the number of lucidophyllous species did not change with distance. Species such as Ficus nipponica, Damnacanthus indicus, Ilex integra, and Lemmaphyllum microphyllum were near-completely or completely limited to the old-growth forest. They are known to be negatively affected by forest fragmentation and were observed to be struggling to colonize the exterior of the old-growth forest even after 60xa0years of abandonment. Their absence highlighted the limited colonization capacities of some old-growth forest species and underlined the time required for habitat restoration following human disturbance. We conclude that it is important to consider the population dynamics of dominant canopy species and the colonization of these interior species when assessing the habitat expansion of lucidophyllous species and hence the restoration of degraded lands.

Trophic Cascades and Food Web Stability in Fish Communities of the Everglades

We introduce the trophic organisation structure of aquatic ecosystems by giving a short overview on some classic landmarks from ecological theory. The concept of trophic cascades describes interactions in food webs that descend the whole structure. They start at the top node of the highest carnivores, the piscivores, by increasing the piscivore’s biomass which in turn triggers changes in the successive trophic hierarchical levels. The concept of trophic cascades has long since passed from theoretical into applied ecology. We demonstrate this with an example of a spatially-explicit simulation model that is used to understand the high variability in the aquatic trophic structure of the Everglades marshland. Changes in hydrology of the Everglades over the last several decades have reduced the hydroperiod in some areas and may have diminished foraging fishes and their food base. A key component for restoring fish productivity to historic levels is to understand and to improve the spatio-temporal water patterns in the wetlands. Therefore, by applying the simulation model we investigated the dynamics of an aquatic food web with the following components: primary producers, detritus, invertebrates, fish consumers and nutrients. For this purpose, a hydroscape of 20 × 20 km was modeled that shows a natural-like elevation gradient. The annual fluctuations in water level were imposed as sinusoidally changing hydrology on the whole system, which resulted in dynamic patterns of flooded and non-flooded areas. We performed long-term simulations over a period of 10 years and examined how the trophic levels reacted to changes in the water level; in particular, how the changing water levels affected trophic cascades. We discuss the consequences of these results for management and restoration of the Everglades aquatic communities.

Modelling the Everglades Ecosystem

The Everglades represent a delicate ecosystem in Southern Florida and is the largest sub-tropical wetland system in the USA. It provides home for a wide variety of unique biodiversity and wildlife. Due to its vicinity to human settlements, the Everglades have been under threat since the beginning of the twentieth century. With the dangers of Global Change on the horizon, this pressure will increase in the near future. The Comprehensive Everglades Restoration Plan (CERP) is a major environmental restoration effort, which is under way and will profoundly affect the Everglades and its neighbouring ecosystems in southern Florida. In the CERP, ecological modelling plays a central role for science-based decision making. In this paper, we introduce the general strategy of modelling for the purpose of ecosystem restoration. We also present two special modelling frameworks and show how they are being used for ecosystem and population-level modelling to help in the planning and evaluation of Everglades restoration.