Population ecology and population recovery programs

by Tibor Hartel

Major proportions of conservation funding goes into population and habitat recovery programs. Changes in population size, community composition or other indicators are employed to ‘demonstrate’ the success of the recovery measures. The time period for implementing such projects and their evaluations is often rather short (say, up to 4-5 years), this probably being constrained by the financial cycle. This may be in ‘conflict’ with the ecological / population cycles of the targeted organism, community or habitat which ‘works’ in different, generally much longer time scale.

Many conservation projects are implemented in areas where the baseline knowledge is rather scarce. Therefore a certain period of time (say two out of the four years) is allocated to describe and understand the ‘status’ of the species, community or habitat at landscape scale. On the basis of this, a plan / strategy is written for the next period to be implemented in order to achieve the desired state of the above mentioned parameters. I think that if not carefully approached, such conservation projects may not achieve their target.

There are some interesting aspects with such projects. Below I mention one, namely the ‘baseline data’ component. This information is used as ‘starting point’ to which further trajectories of the system are related and ultimately the ‘success’ of the project will be inferred.

I will use my own 15 year study on Agile Frog (Rana dalmatina) in a semi natural pond from Southern Transylvania to illustrate this situation. Egg masses were counted and used as proxy for (female) population size, with the assumption that each female deposit one egg mass in each spring. The results are presented in the Figure 1. First, it seems that there is no trend in this population and calculations show that the population is regulated by its own density and an important other variable is the weather condition in early spring which probably affect winter survival.

Figure 1. Fluctuation of egg mass number of Rana dalmatina in 15 year period in a semi natural pond from Southern Transylvania.

If we consider three years for assessing the state of this population and then to develop some management strategies, we may have different results, depending on where this three years of study is carried out. If it happens to be 2000-2002 or 2009-2011, then we may conclude a sharp decline in population size and urge the need for recovery plans. If we look for the 2003-2005 or the 2007-2009 periods, the population seems to do well, explosively increase. If we consider the overall, 15 year period, no trend is apparent. What is a good reference point, therefore?

But I can move even further – not because I want to complicate life, but because there is much empirical evidence that such situations may occur (see the many papers about the ‘ability’ of natural systems to ‘shift’ between many equilibrium states). Below I present some ‘made up’ data, a hypothetical example. Let’s assume that this frog population is monitored since my great-grandmother’s time and we have an excellent database about the very long term population fluctuation.

Figure 2 show such an imaginary situation.

Figure 2. Hypothetical population fluctuation of Rana dalmatina through multiple decades. This are made up data, just to illustrate a possible situation. The story below is also invented. My great-grandmother started this imaginary monitoring project. The population increased e.g. because a stable pond appeared (instead of the river floodplain) without fish. Moreover the vegetation growth increased, transforming the pond into a real ‘frog nursery’ (as noted by her). After some decades, the population size stabilized. My grandfather was unable to detect why this happened, and he speculated: probably the carrying capacity of the environment was reached. He also noted that goldfish was introduced in the pond, but without any visible effect. My father continued the egg mass counts: he noticed a decrease in frog population size. Some increase of the vegetation cover was also noticed and that there are less egg masses in densely vegetated areas of the pond. I studied the pond for 15 years (marked with yellow) and cannot demonstrate any trend in population size. It seems that the population is stable, yet widely fluctuating (see Figure 1 for real data).

This figure shows two stability states for the same (hypothetical) population for quite long periods and within both states it was a wide fluctuation. Which state we should use as ‘reference point’ for our restoration activity? What type of further trajectory is desired for this population? What is the time lag between intervention and population response? Who should be involved (i.e. stakeholders) in such a project in short term and in long term?

I cannot offer a ‘black and white’ solution for this problem. However, this doesn’t mean that we close our eyes to it and I like to share my thoughts on it here.

First, probably the funding institutions should be more aware about what they ask from nature resource managers, and ‘relax’ their expected goals e.g. by paying more attention to unpredicted changes. For example, expectations like ‘increasing frog population size to 500 in the next five years’ may not be realistic in long term, because populations fluctuate and we don’t know (or rarely know) the multiple reasons of fluctuations. For example, a short term research may show negative association between certain fish species and amphibians (e.g. our studies published in Hydrobiologia and Environmental Conservation). Removal of fish species can be a good short term goal (i.e. it can be realized in short time period) but the increase of the Great Crested Newt population to a certain population in three years after this implication may not be a realistic expectation.

Second, conservation institutions and organizations may put more emphasis in their strategies on the spatio-temporal dynamic of populations and communities and to include the possibility for unexpected changes. Population increase of a target species is always a good thing. But before celebrating, don’t forget that the increase may not be caused by restoration activity but is ‘purely’ a population process that would have happened anyway. Contrary, population decrease may not reflect the failure of the restoration project but was caused by other reasons. However, conservation leaders need to be sure that the interventions were made based on the best available knowledge and also attitude.

Put more emphasis on high profile research. Spatial ecological studies may help in identifying potential source and sink habitats and populations and the optimal ‘habitat profile’ for a particular region. A risk assessment can be made in order to identify landscape elements under ‘threat’ and to develop conservation strategies for them – not forgetting that there may be always unexpected outcomes, not controllable by managers in short term. For example, Solidago canadensis is an ‘aggressive’ invasive plant in Europe. It can be highly abundant at landscape and regional level – as it is in the Saxon area of Transylvania. Spatial ecological models may help in understanding limits and possibilities of eradication projects, before these started. Results may show that eradication is financially and logistically not feasible because it should be implemented at regional scale. However, an other option may be that (i) understand which factors contribute to its spread and (ii) manage the ‘Solidago novel ecosystems’ in a way to maximize them for native species.

In an ideal world, funds should be available for long term monitoring projects. This need is maybe higher now then ever was before.

Assure ‘continuity’ of the project. Institutions may change, leaders may change, and public attitude may change. However, this change should not affect the long term vision established in the project. In fact, leaders and managers could influence change e.g. by clever involvement of stakeholders. This is why I feel it is important to have a good, conflict free starting point, with all the key stakeholders involved in sharing this vision and developing short and long term goals in order to achieve them. Ultimately, each restoration activity should be a social event and fill a social need. Depending on the leadership, multiple stakeholders may realize this – or not. This all may sound ambitious, but still is better to try a hard step in this way instead of showing how beautiful our (expensive) project was in short term – but not viable in long term.


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