Thursday, December 4, 2014

Watching Extinction Happen? A Crash of B. citrinus

There are some people who love to watch things go extinct. I'm not one of them. But there are folks who so dislike and abhor the federal regulations that surround wildlife protection - this implies federal control over what you can and cannot do on your property should a species of concern be identified on your land - that they actually hope and pray that things go extinct before anyone finds out they even existed.  Ignorance is bliss, and sometimes profitable. I count among my friends a certain business person who says "Hey, extinction is a good thing! It means I don't have to worry about some butterfly or mouse that no one cares about closing me down." That's one side to an economic argument for extinction.

Some colleagues of mine working on voucher collections to establish historic presence of species. Joan is a superb citizen scientist from West Virginia who can ID wild bee circles around the rest of us! (W. Virginia)

So what does a beekeeper think about this? Or an orchard manager? Or an architect who also happens to be an ecologist? What if the scientist is also a farmer: a commercial horticulturalist, or a sheep farmer, or someone who holds a PhD in marine fisheries while managing a very large poultry business? I know these folks, too. And contrary to my friend "The Strict Economist," there is room for the farmer-scientist in this discussion and the science can get pretty dense pretty quick.

Alex is a commercial beekeeper as well as a pollination ecologist. Bumble bees are not easy to catch in pan traps, so it's the old fashioned sweep net for us. (Adams Co. PA)

To say that a species is rare or endangered and on its way to extinction is a complicated idea with a lot of moving parts. It is also, for a lot of people, an emotional issue.  But let's consider the problem as a biological issue. Think metapopulation biology - the study of local populations linked by the ability of individuals to move across a large range. Also consider  population dynamics, something we don't even know much about in bumble bees yet.  As restoration ecologist and de-extinction scientist Kevin Kelly said "We really don't know anything about nature. But we do know that we have a duty to understand it."  I think we need many more young people in the natural sciences!

It's difficult to ascertain if a bee species is near extinction when you only have a relatively few surveys of relatively few sites when you consider the size of a range - even in a small state. We need more people to help with the field work!  (Delaware)

Within a metapopulation biological framework we need to consider the probabilities of extinction, that in the very big picture depends on what the organism is - a plant, insect, mammal. bird, reptile? So we learn that we have an insect in danger of dying out - a bee.  When the folks hear about this the conversation goes something like this:

"Oh. We're talking about a bee!" (Extinction is bad.) "What can I do to stop it from happening on my farm because - I need bees!" (Save The Bees!)

"A native bee?"  (Save The Native Pollinators! Say No To Extinction!) 

"A bumble bee?!" (Save the Warm, Cuddly, Fuzzy-Wuzzy Flying Teddybear!)

"Wait - you say it's a parasitic bumble bee?!!" (WHOA! A parasite?! Isn't that different?)

"It's a nest parasite to one of our most highly effective native bumble bees on agricultural lands? What the - ? Come on." (Oh. Definitely Bad. Let It Go. Extinction OK!)

Bombus Psithyrus citrinus. Photo: John Asher

So this morning as emails were a-flying with the results from the latest compilation of bumble bee survey data up to and including 2014, several researchers pointed out a startling crash. I mean, emails started really flying - and text messages - and Twitter. I sat at my home office desk shaking my head. The data tables showed that Bombus Psithyrus citrinus, the lemon cuckoo bumble bee, was not only becoming more rare over twenty years of survey data in all states but that this year there were no records of it at all. Emails kept flying all day. No records.

Bombus impatiens, the host bee. (Avondale, PA)

Cuckoo bumble bees do not produce workers of their own, but they do lay their eggs in the nests of host bumble bees, mostly B. impatiens and B. vagrans - pretty bumble bees common to our area. The host bee populations seem to be doing just fine, however, according to our survey data. What we know of this situation is that there is a big drop in numbers of collected B. citrinus across its entire historic range. So big that over the past ten years, numbers of B. citrinus spiraled down to zero. That's 0.  I am monitoring B. terricola, a species of concern across its entire range as well, so I always scan the annual survey reports and I know that some years are better than others and that in different areas survey results can vary from frighteningly low to doing just fine. But I've never seen a zero in any of these reports for any species.

I spent every summer weekend in 2011 along the Kancamagus Highway in the White Mountains finding lots of B. terricola - where they shouldn't have been! Have we been looking in all the wrong places?  (New Hampshire)

Is this event indicating widespread or local declines? We really don't know how widespread an extinction event has become until we know a species' full range. We need more people in the field watching - and if they are trained to collect and identify, we can learn more. I know a lot of folks who help with this sort of thing but they can't cover all the range in all of a landscape so complex. Additionally we just don't know if there are source sites of B. citrinus population that could re-establish populations in areas that have become sinks - areas of loss. If we find source sites can we put protections on them so that sinks can be recolonized? What if the property is privately owned? Do federal rules apply if an insect species of concern is found on private land? For a "just a" parasitic bee? It certainly doesn't have the charismatic  value of say a polar bear or an elephant.

Sam prepares to train another eager class for wild bee ID at the National Conservation Training Center in West Virgina.

I looked again at the data, this time a little differently. To compare this situation with a host and a disease, over time the host very well could develop a certain immunity to it. If populations of B. impatiens are strong, would this indicate that the host bumble bee has developed some sort of defense against the nest parasite? And if it has, will we see a bump in B. impatiens population?  Many hosts and parasites seem to exist in a state of equilibrium until the host evolves a more effective defense. In some parasitized but isolated populations in a fragmented range  there are cases of repeated extinctions of the parasite or disease over time  as the host develops defenses or immunities. Is this where we are  B. citrinus?  Are we right to be worried, or is this a natural high/low/zero relationship? If a natural die-out, we know, too, that populations of host organisms may lose resistance or immunity if the parasite has been out of picture for a very long time and when the disease or parasite returns (recolonizes) the host population dips in response. If this is the case with B. impatiens and vagans, will these host populations crash if and when the lemon cuckoo bumble bee makes a comeback? Oh, my brain! 

The Mid-Atlantic is a HUGE matrix of complex landscapes in which to look for a single species of bee. But if we are to find out what is happening to the lemon cuckoo bumble bee, we need more people looking! (Pine Barrens, NJ)

This parasitic bee is crashing. Should we worry? If it matters to us, what should we do? If we let "nature take its course" what are the consequences of letting the bee go? Three important things to remember while considering these questions:
  1. Scale matters. We need to be able to see in terms of metapopulations and involve people especially citizen scientists and students in the field work required to understand the dynamics of large ranges.
  2.  Local extinctions and recolonization happen normally and naturally,  because ...
  3.  Creatures, like bees, can move across ranges, and...
  4.  Parasitic species have dynamics of their own that we know very little about.


Fact sheet and distribution data on B. citrinus:

The following  article by Williams, Colla, and Xie (2009) - some of the people sending email this morning, describe important U.K.-based research in Bombus vulnerability. This is very interesting to me, considering the U.K.'s island-like biogeography, it's northern aspect, and that climate change and habitat fragmentation are "easier" to make actual parameters (unlike the big, broad, complex landscape of the continental U.S.) This piece gives an idea of some of the difficulties in determining species status through metapopulation studies and population dynamics:

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